Use llvm::DeleteContainerSeconds when possible

llvm-svn: 201739
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index d617b36..8d46a8f 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -191,10 +191,7 @@
 };
 
 void ASTUnit::clearFileLevelDecls() {
-  for (FileDeclsTy::iterator
-         I = FileDecls.begin(), E = FileDecls.end(); I != E; ++I)
-    delete I->second;
-  FileDecls.clear();
+  llvm::DeleteContainerSeconds(FileDecls);
 }
 
 void ASTUnit::CleanTemporaryFiles() {