Revert "[Coverage] Ignore unused functions if the count is 0." (#107901)

Reverts #107661

Breaks llvm-project/llvm/unittests/ProfileData/CoverageMappingTest.cpp

Author: ZequanWu

compiler-rt/test/profile/instrprof-merging-2.cpp

@@ -851,7 +851,7 @@ Error CoverageMapping::loadFunctionRecord(
   // won't (in which case we don't unintuitively report functions as uncovered
   // when they have non-zero counts in the profile).
   if (Record.MappingRegions.size() == 1 &&
-      Record.MappingRegions[0].Count.isZero())
+      Record.MappingRegions[0].Count.isZero() && Counts[0] > 0)
     return Error::success();
 
   MCDCDecisionRecorder MCDCDecisions;