Unify LevelDB.*Options.

We have seven different types all called like LevelDB.*Options.  One
of them is the plain LevelDBOptions. All others are just wrapping that
type without adding anything except clunkier handling.

If there ever was a plan to add more specific options to the various
LevelDB.*Options types, history has proven that nothing like that is
going to happen anytime soon.

To keep the code a bit shorter and more focused on the real (quite
significant) complexities we have to deal with here, this commit
reduces all uses of LevelDBOptions to the actual LevelDBOptions type.

1576 fewer characters to read...

Change-Id: I3d7a2b7ffed78b337aa37f812c53c058329ecaa6
Merge "Unify LevelDB.*Options."