Simplify codes for BuildSuperImage func

Use common function LoadDictionaryFromFile(), instead
of LoadDictionaryFromLines(). Makes these codes conciser.

Change-Id: Ibb6f19744246b3415bcd639bc59dbb2aede725d9
Signed-off-by: jiajia tang <tangjiajia@xiaomi.com>

tools/releasetools/build_super_image.py

@@ -194,10 +194,8 @@ def BuildSuperImage(inp, out):
       return BuildSuperImageFromTargetFiles(inp, out)
 
     if os.path.isfile(inp):
-      with open(inp) as f:
-        lines = f.read()
       logger.info("Building super image from info dict...")
-      return BuildSuperImageFromDict(common.LoadDictionaryFromLines(lines.split("\n")), out)
+      return BuildSuperImageFromDict(common.LoadDictionaryFromFile(inp), out)
 
   raise ValueError("{} is not a dictionary or a valid path".format(inp))