test: db: fix test to have a smaller timeout for when it runs on faster hardware
Update timeout to 50ms instead of 3.
Compact SpatialDB as we go, not at the end
remove_internal_filter_policy

Summary:
1. remove class InternalFilterPolicy in db/dbformat.h
2. Transformation from internal key to user key is done in filter_block.cc
3. This is a preparation for patch D20979

Test Plan:
make all check
valgrind ./db_test

Reviewers: igor, yhchiang, ljin, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22509
Merge pull request #237 from tdfischer/tdfischer/faster-timeout-test

test: db: fix test to have a smaller timeout for when it runs on faster ...