BaseTools: refactor and remove un-needed use of .keys() on dictionaries

sometimes just delete it.
sometimes the loop needed .values() instead

Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>

BaseTools/Source/Python/Common/String.py

@@ -1,7 +1,7 @@
 ## @file
 # This file is used to define common string related functions used in parsing process
 #
-# Copyright (c) 2007 - 2015, Intel Corporation. All rights reserved.<BR>
+# Copyright (c) 2007 - 2018, Intel Corporation. All rights reserved.<BR>
 # This program and the accompanying materials
 # are licensed and made available under the terms and conditions of the BSD License
 # which accompanies this distribution.  The full text of the license may be found at
@@ -110,7 +110,7 @@ def GetSplitList(String, SplitStr=DataType.TAB_VALUE_SPLIT, MaxSplit= -1):
 # @param Arch:  The Arch to be added or merged
 #
 def MergeArches(Dict, Key, Arch):
-    if Key in Dict.keys():
+    if Key in Dict:
         Dict[Key].append(Arch)
     else:
         Dict[Key] = Arch.split()