[Triton-MLIR][Testing]Fix tests warning, with small code clean-up (#894)

1.Code clean-up to remove superfluous #includes.
2.Fix two python test warnings, in which one relates to ["#"
formats](https://jira.mongodb.org/browse/PYTHON-2343), the other relates
to regular expression string usage.

include/triton/Target/LLVMIR/LLVMIRTranslation.h

@@ -2,6 +2,7 @@
 #define TRITON_TARGET_LLVMIRTRANSLATION_H
 #include "llvm/ADT/StringRef.h"
 #include <memory>
+#include <string>
 #include <vector>
 
 namespace llvm {

include/triton/Target/PTX/PTXTranslation.h

@@ -1,7 +1,6 @@
 #ifndef TRITON_TARGET_PTXTRANSLATION_H
 #define TRITON_TARGET_PTXTRANSLATION_H
 
-#include <memory>
 #include <string>
 
 namespace llvm {