Is libsqlite3-sys really needed?

Hello,

I know proj requires sqlite3 for some of it's functionality. However, I'm not sure it exposes any of that to the external world.

My question is: do we really need this:

https://github.com/georust/proj/blob/main/proj-sys/Cargo.toml#L15

The extern crate is defined only under the `bundled_build` cfg:

https://github.com/georust/proj/blob/main/proj-sys/src/lib.rs#L31

and I think that cfg is disabled by default.

The reason I'm asking is that I want to have both `proj` and `rusqlite` and I get

Using `proj = 0.29` (I know `0.30` is most recent, but because of some nix stuff, I'm forced to use `0.29`) and `rusqlite=0.36.0`, I get this error:

```
error: failed to select a version for `libsqlite3-sys`.
... required by package `proj-sys v0.25.0`
... which satisfies dependency `proj-sys = "^0.25.0"` of package `proj v0.29.0`
... which satisfies dependency `proj = "^0.29.0"` of package `binaries v0.1.0 (xxx/binaries)`
versions that meet the requirements `>=0.28, <0.31` are: 0.30.1, 0.30.0, 0.29.0, 0.28.0

package `libsqlite3-sys` links to the native library `sqlite3`, but it conflicts with a previous package which links to `sqlite3` as well:
package `libsqlite3-sys v0.34.0`
... which satisfies dependency `libsqlite3-sys = "^0.34.0"` of package `rusqlite v0.36.0`
... which satisfies dependency `rusqlite = "^0.36.0"` of package `xxx v0.1.0 (/xxx)`
... which satisfies path dependency `xxx` (locked to 0.1.0) of package `binaries v0.1.0 (xxx/binaries)`
Only one package in the dependency graph may specify the same links value. This helps ensure that only one copy of a native library is linked in the final binary. Try to adjust your dependencies so that only one package uses the `links = "sqlite3"` value. For more information, see https://doc.rust-lang.org/cargo/reference/resolver.html#links.

failed to select a version for `libsqlite3-sys` which could resolve this conflict
```

Inspect the dependency at proj-sys/Cargo.toml and the bundled_build-gated extern crate in proj-sys/src/lib.rs. Reproduce the resolver conflict with proj 0.29 and rusqlite 0.36, then determine whether the libsqlite3-sys dependency is required and verify that the dependency graph resolves without duplicate sqlite3 links.

Written by the indexing model from the issue text.