Simplify codes when _LoadOemDicts

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

Signed-off-by: jiajia tang <tangjiajia@xiaomi.com>
Change-Id: I15d6d4281a03be8a2f6f855054b1e4c1c3010fcd
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 43c39fb..3c0fd34 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -543,8 +543,7 @@
 
   oem_dicts = []
   for oem_file in oem_source:
-    with open(oem_file) as fp:
-      oem_dicts.append(common.LoadDictionaryFromLines(fp.readlines()))
+    oem_dicts.append(common.LoadDictionaryFromFile(oem_file))
   return oem_dicts