BaseTools: cleanup LongFilePathSupport usage

1) remove an identical function and import it from Common.LongFilePathSupport
2) remove an import that is not needed/used.

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 : Bob Feng <bob.c.feng@intel.com>

BaseTools/Source/Python/build/build.py

@@ -36,7 +36,6 @@ from subprocess import *
 from Common import Misc as Utils
 
 from Common.LongFilePathSupport import OpenLongFilePath as open
-from Common.LongFilePathSupport import LongFilePath
 from Common.TargetTxtClassObject import *
 from Common.ToolDefClassObject import *
 from Common.DataType import *