Revert "[Coverage] Revise format to reduce binary size"

This reverts commit e18531595bba495946aa52c0a16b9f9238cff8bc.

On Windows, there is an error:

http://lab.llvm.org:8011/builders/sanitizer-windows/builds/54963/steps/stage%201%20check/logs/stdio

error: C:\b\slave\sanitizer-windows\build\stage1\projects\compiler-rt\test\profile\Profile-x86_64\Output\instrprof-merging.cpp.tmp.v1.o: Failed to load coverage: Malformed coverage data

1 files changed, 0 insertions, 2 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
index ca777b6..8d5e56e 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
@@ -804,8 +804,6 @@ static std::string getCoverageMapErrString(coveragemap_error Err) {
     return "Truncated coverage data";
   case coveragemap_error::malformed:
     return "Malformed coverage data";
-  case coveragemap_error::decompression_failed:
-    return "Failed to decompress coverage data (zlib)";
   }
   llvm_unreachable("A value of coveragemap_error has no message.");
 }