[Utils] Remove an unused local variable (NFC) (#168181)

Identified with bugprone-unused-local-non-trivial-variable.

Author: kazutakahirata

llvm/unittests/Transforms/Utils/LocalTest.cpp

@@ -679,7 +679,6 @@ TEST(Local, FindDbgRecords) {
   findDbgUsers(Arg, Records);
   EXPECT_EQ(Records.size(), 1u);
 
-  SmallVector<DbgValueInst *> Vals;
   Records.clear();
   // Arg (%a) is used twice by a single dbg_assign. Check findDbgValues returns
   // only 1 pointer to it rather than 2.