[bug] conan info displays build requirements even though documentation states otherwise

When executing **conan info** on a conanfile also the packages in the build requires section are displayed. This also applies to transitive build requirements.

The documentation states, that build requirements are ignored by [conan info](https://docs.conan.io/en/latest/devtools/build_requires.html#properties-of-build-requirements).
Specifically it states this:

> Build requirements are not listed in conan info nor are represented in the graph (with conan info --graph).

My expectation is that conan info ignores all build requirements.

### Environment Details
* Operating System+version: Ubuntu 16.04
* Conan version: 1.22.2
* Python version: 3.5.2

### Steps to reproduce
conanfilea.txt
```
[requires]
boost/1.71.0@conan/stable
example/1.0.0@user/test

[build_requires]
cmake_installer/3.16.1@conan/stable

[generators]
cmake
```

conanfileb.py
```python
from conans import ConanFile
import os
class ExampleConan(ConanFile):
name = "example"
version = "1.0.0"
license = "mylicense"
settings = "os", "compiler", "build_type", "arch"
generators = "cmake"
requires = (
"zlib/1.2.11@conan/stable"
)
build_requires = "cmake_installer/3.15.3@conan/stable"

def build(self):
pass

def package(self):
pass
```

Then execute the following:
```bash
conan create conanfileb.py user/test && conan info conanfilea.txt -db
```

### Logs

Note that cmake_installer appears in both versions in the output.
That means, that the build requirement from the conanfilea.txt as well as the trasntive build requirement from conanfileb.py are displayed.

```bash
root@0da710da3a0e:/tmp# conan create conanfileb.py user/test && conan info conanfilea.txt -db
bzip2/1.0.8@conan/stable: Forced build from source
zlib/1.2.11@conan/stable: Forced build from source
boost/1.71.0@conan/stable: Forced build from source
example/1.0.0@user/test: Forced build from source
cmake_installer/3.15.3@conan/stable: Forced build from source
cmake_installer/3.16.1@conan/stable: Forced build from source
conanfilea.txt
ID: affe26b56e2352e50699aa6b2d376fb2b28a2cde
BuildID: None
Requires:
boost/1.71.0@conan/stable
example/1.0.0@user/test
Build Requires:
cmake_installer/3.16.1@conan/stable
boost/1.71.0@conan/stable
ID: 6a6207f6b8ad5cd355e8292e4efe81c5ae8e97f1
BuildID: None
Remote: COMPANYSERVER
URL: https://github.com/lasote/conan-boost
License: Boost Software License - Version 1.0. http://www.boost.org/LICENSE_1_0.txt
Recipe: Cache
Revision: 0
Binary: Build
Binary remote: None
Creation date: 2019-09-14 11:19:31
Required by:
conanfilea.txt
Requires:
zlib/1.2.11@conan/stable
bzip2/1.0.8@conan/stable
bzip2/1.0.8@conan/stable
ID: 3df6ebb8a308d309e882b21988fd9ea103560e16
BuildID: None
Remote: COMPANYSERVER
URL: https://github.com/conan-community/conan-bzip2
Homepage: http://www.bzip.org
License: bzip2-1.0.8
Author: Conan Community
Topics: conan, bzip2, data-compressor, file-compression
Recipe: Cache
Revision: 0
Binary: Build
Binary remote: None
Creation date: 2019-08-20 09:27:12
Required by:
boost/1.71.0@conan/stable
cmake_installer/3.15.3@conan/stable
ID: 44fcf6b9a7fb86b2586303e3db40189d3b511830
BuildID: None
Remote: COMPANYSERVER
URL: https://github.com/conan-community/conan-cmake-installer
Homepage: https://github.com/Kitware/CMake
License: BSD-3-clause
Author: Conan Community
Topics: conan, cmake, build, installer
Recipe: Cache
Revision: 0
Binary: Build
Binary remote: None
Creation date: 2019-11-01 09:42:59
Required by:
example/1.0.0@user/test
cmake_installer/3.16.1@conan/stable
ID: 44fcf6b9a7fb86b2586303e3db40189d3b511830
BuildID: None
Remote: COMPANYSERVER
URL: https://github.com/conan-community/conan-cmake-installer
Homepage: https://github.com/Kitware/CMake
License: BSD-3-clause
Author: Conan Community
Topics: conan, cmake, build, installer
Recipe: Cache
Revision: 0
Binary: Build
Binary remote: None
Creation date: 2020-01-27 06:58:08
Required by:
conanfilea.txt
example/1.0.0@user/test
ID: 48cd815bc80e20569acd9d2a2a3973827691aa1e
BuildID: None
Remote: None
License: mylicense
Recipe: Cache
Revision: d339af35c002e3dcc595911400c13cdd
Binary: Build
Binary remote: None
Creation date: 2020-02-19 09:57:35
Required by:
conanfilea.txt
Requires:
zlib/1.2.11@conan/stable
Build Requires:
cmake_installer/3.15.3@conan/stable
zlib/1.2.11@conan/stable
ID: 76f87539fc90ff313e0b3182641a9bb558a717d2
BuildID: None
Remote: COMPANYSERVER
URL: http://github.com/conan-community/conan-zlib
Homepage: https://zlib.net
License: Zlib
Author: Conan Community
Topics: conan, zlib, compression, zip
Recipe: Cache
Revision: 0
Binary: Build
Binary remote: None
Creation date: 2019-09-04 19:48:42
Required by:
boost/1.71.0@conan/stable
example/1.0.0@user/test
```