TW-88158: remove MercurialCommitsInfoBuilderSupport and CommitsAndMountPointsCommand together with the custom hg extension. - The extension point was introduced for Upsource and is no longer needed. - The hg extension was not compatible with python 3 and led to test errors. (grafted from cb5e6f9a2bcd450e660c89305b190f5ed272e0d6)

<component name="libraryTable">
  <library name="JUnit">
    <CLASSES>
      <root url="jar://$PROJECT_DIR$/mercurial-tests/lib/junit-3.8.1.jar!/" />
    </CLASSES>
    <JAVADOC />
    <SOURCES />
  </library>
</component>