batteryservice: remove unneeded catch clause and fix build

The IOException clause already catches the FNF one.
Also in 9f8e6008 the import for
FNF got removed, fix the build.

Change-Id: Iaa8bc77b5191ca6abb62e2ea51fd54614ab3c53b
Signed-off-by: Alexander Martinz <eviscerationls@gmail.com>