Revert the default setting of InitFromCmdLineArgs().

Summary:
Revert the default setting of InitFromCmdLineArgs() as all the callers
currently provide full set of arguments.

Test Plan:
make reduce_levels_test
./reduce_levels_test

Reviewers: haobo, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19257