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

This reverts commit 99317124e1c772e9a9de41a0cd56e1db049b4ea4. This is
still busted on Windows:

http://lab.llvm.org:8011/builders/lld-x86_64-win7/builds/40873

The llvm-cov tests report 'error: Could not load coverage information'.

1 files changed, 0 insertions, 2 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
index 70f00d3..9d39b7c 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
@@ -805,8 +805,6 @@ 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.");
 }