Do not remove resource messages in Xml tests (#81463)

Do not remove resource messages in Xml tests (#81463)

Addresses first bullet of #81455.

Addresses 211 test failures to the tune of:

```
[FAIL] System.Xml.XmlSchemaValidatorApiTests.TCValidateWhitespace_String.WhitespaceInsideElement
System.Xml.Tests.VerifyException : GetManifestResourceStream() failed
   at System.Xml.Tests.ExceptionVerifier..ctor(String assemblyName, ExceptionVerificationFlags flags, ITestOutputHelper output) + 0x4c9
   at System.Xml.XmlSchemaValidatorApiTests.TCValidateWhitespace_String..ctor(ITestOutputHelper output) + 0x48
```