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/tools/libclang/CXString.h b/tools/libclang/CXString.h
index d36c7c1..c354bd2 100644
--- a/tools/libclang/CXString.h
+++ b/tools/libclang/CXString.h
@@ -23,7 +23,7 @@
 namespace cxstring {
   
 struct CXStringBuf {
-  llvm::SmallString<128> Data;
+  SmallString<128> Data;
   CXTranslationUnit TU;
   CXStringBuf(CXTranslationUnit tu) : TU(tu) {}
 };