Remove unmapped histogram GPU.BlockStatusForClient3DAPIs

It was never added to histograms.xml

BUG=643546

Review-Url: https://codereview.chromium.org/2338363004
Cr-Commit-Position: refs/heads/master@{#418903}

content/browser/gpu/gpu_data_manager_impl_private.cc

@@ -1228,11 +1228,6 @@ GpuDataManagerImplPrivate::Are3DAPIsBlockedAtTime(
     // Err on the side of caution, and assume that if a particular
     // domain shows up in the block map, it's there for a good
     // reason and don't let its presence there automatically expire.
-
-    UMA_HISTOGRAM_ENUMERATION("GPU.BlockStatusForClient3DAPIs",
-                              BLOCK_STATUS_SPECIFIC_DOMAIN_BLOCKED,
-                              BLOCK_STATUS_MAX);
-
     return GpuDataManagerImpl::DOMAIN_BLOCK_STATUS_BLOCKED;
   }