Remove ValidateAssemblyVersionsInRefPack target

The only thing this target did was a redundant check that AssemblyVersion was
set for projects in the Targeting Pack.  That check was failing for
the NETStandard build of System.DirectoryServices.

This target was providing no value, instead we need to fix #42961
which will be a proper check of our servicing version rules.

Author: ericstj

eng/packaging.targets

@@ -318,12 +318,6 @@
     </ItemGroup>
   </Target>
 
-  <Target Name="ValidateAssemblyVersionsInRefPack"
-          Condition="'$(SkipValidateAssemblyVersion)' != 'true' and '$(_AssemblyInTargetingPack)' == 'true' and '$(PreReleaseVersionLabel)' == 'servicing'"
-          AfterTargets="CoreCompile" >
-    <Error Condition="'$(AssemblyVersion)' != '$(LastReleasedStableAssemblyVersion)'" Text="AssemblyVersion should match last released assembly version $(LastReleasedStableAssemblyVersion)" />
-  </Target>
-
   <Target Name="ValidateServicingVersionIsProperlySet"
           Condition="'$(PreReleaseVersionLabel)' == 'servicing' and
                      '$(PackageUseIncrementalServicingVersion)' == 'true' and