[gn] fix mistake from 92289db

Author: nico

llvm/utils/gn/secondary/llvm/unittests/IR/BUILD.gn

@@ -52,6 +52,6 @@ unittest("IRTests") {
     "VectorBuilderTest.cpp",
     "VectorTypesTest.cpp",
     "VerifierTest.cpp",
-    "VFABIDemanglerTest.cpp,"
+    "VFABIDemanglerTest.cpp",
   ]
 }