drop more llvm:: prefixes on SmallString<>

More cleanup after r149799.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150380 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/Basic/SourceManagerTest.cpp b/unittests/Basic/SourceManagerTest.cpp
index 5887211..14f5b22 100644
--- a/unittests/Basic/SourceManagerTest.cpp
+++ b/unittests/Basic/SourceManagerTest.cpp
@@ -97,7 +97,7 @@
   ASSERT_TRUE(macroExpStartLoc.isFileID());
   ASSERT_TRUE(macroExpEndLoc.isFileID());
 
-  llvm::SmallString<32> str;
+  SmallString<32> str;
   ASSERT_EQ("M", PP.getSpelling(macroExpStartLoc, str));
   ASSERT_EQ(")", PP.getSpelling(macroExpEndLoc, str));