Remove "using namespace llvm" from ReleaseModeModelRunner.h

A using directive in a header pollutes the namespace of all files which
include that header. It seems this snuck in in D115764 by moving some
code from a cpp file.

Author: labath

llvm/include/llvm/Analysis/ReleaseModeModelRunner.h

@@ -20,7 +20,6 @@
 #include <memory>
 #include <vector>
 
-using namespace llvm;
 namespace llvm {
 
 /// ReleaseModeModelRunner - production mode implementation of the