IndexedDB: Remove unused unit test file

Was removed from gypi but the file was still around. The tests
now live in Chromium's indexed_db_database_unittest.cc

BUG=234278
TBR=jamesr@chromium.org
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/19705009

git-svn-id: svn://svn.chromium.org/blink/trunk@154540 bbb929c8-8fbe-4397-9dbb-9b2b20218538