Fix incorrect explanation about VS xml coverage file format for CFamily

The coverage documentation states 
`sonar.cfamily.vscoveragexml.reportsPath`|Path may be absolute or relative to the solution directory. Path wildcards (see above) are supported. Note that the `.coveragexml` report format offered by Visual Studio is not supported.

This is incorrect. The unsupported format is `.coverage`. This format can be converted into the supported `.coveragexml` with the MS tool CodeCoverage.exe as seen in
https://community.sonarsource.com/t/ms-coverage-coveragexml/21494

Also note that this is only for CFamily coverage. The same coverage format is documented in the .NET section without mentioning .vscoverage or .vscoveragexml