BaseTools: refactor and remove out of date use of .keys()

this is no longer required to make dictionary objects iterable.

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/GenFds/Section.py

@@ -111,10 +111,7 @@ class Section (SectionClassObject):
     #   @retval tuple       (File list, boolean)
     #
     def GetFileList(FfsInf, FileType, FileExtension, Dict = {}, IsMakefile=False):
-        if FileType in Section.SectFileType.keys() :
-            IsSect = True
-        else :
-            IsSect = False
+        IsSect = FileType in Section.SectFileType
 
         if FileExtension is not None:
             Suffix = FileExtension