BaseTools: Replace StringIO.StringIO with io.BytesIO

Replace StringIO.StringIO with io.BytesIO to be compatible with python3.
This commit also removes "import StringIO" from those python scripts
that don't really use it.

Contributed-under: TianoCore Contribution Agreement 1.1
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>

BaseTools/Source/Python/AutoGen/IdfClassObject.py

@@ -14,7 +14,6 @@
 # Import Modules
 #
 import Common.EdkLogger as EdkLogger
-import StringIO
 from Common.BuildToolError import *
 from Common.StringUtils import GetLineNo
 from Common.Misc import PathClass