Transformation doubles in "expanded" representation for pxrUsdReferenceAssembly

**Describe the bug**
Logging on behalf of Pixar - When a pxrUsdReferenceAssembly is set to the "Expanded" representation and it references another model, the transform appears to be doubled on the referenced model.

**Steps to reproduce**
1. Download the following files under Attachments and convert them to .usda (unfortunately, I was unable to upload .usda files).

2. Run the following maya commands (you may need to update the path of the CubeOuter.usda file depending on where you have stored it).
```
import maya.cmds as cmds

cmds.loadPlugin('pxrUsd', quiet=True)

usdFile = os.path.abspath('CubeOuter.usda')
primPath = '/Outer_prop'

assemblyNode = cmds.createNode('pxrUsdReferenceAssembly', name='Outer')
cmds.setAttr("%s.filePath" % assemblyNode, usdFile, type="string")
cmds.setAttr("%s.primPath" % assemblyNode, primPath, type="string")

```
3. Right click on the top level node named "Outer", select Scene Assembly -> Expanded.

The green cube appears to be at tx=10 ty=4. We would expect the cube to be at tx=5 ty=2. We are able to achieve the expected result when switching to Full or Collapsed. There may be something in the proxyShape code that is leading to the double transform.

Also, the transformation is doubled even if only one of the transformations is applied (ex, if only ty=2 is applied to the referenced model or tx=5 is applied within the referenced model).

**Attachments:**
Referenced model with tx=5 applied: [CubeInner.txt](https://github.com/Autodesk/maya-usd/files/6804818/CubeInner.txt)
Model that references CubeInner.usda and applies ty=2 to it. [CubeOuter.txt](https://github.com/Autodesk/maya-usd/files/6804819/CubeOuter.txt)

Pixar JIRA MAYA-3007

Start by reproducing the issue with the provided Maya commands and the CubeInner.txt and CubeOuter.txt attachments, converting them to .usda as described. Then inspect the proxyShape code mentioned in the report; done means the Expanded representation places the referenced cube at tx=5, ty=2, matching Full and Collapsed rather than doubling either transform.

Written by the indexing model from the issue text.