[Instrumentation] Remove an unused local variable (NFC) (#138383)

diff --git a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
index b1d96db..0346785 100644
--- a/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
@@ -1938,8 +1938,6 @@
 }
 
 void InstrLowerer::emitNameData() {
-  std::string UncompressedData;
-
   if (ReferencedNames.empty())
     return;