Remove older vbucket files

These changes are done as a separate commit in order to make the
previous vbucket fork/refactor as restricted as possible to the vbucket
code itself.

Changes:

- Remove references to vb-aliases.h and libvbucket/vbucket.h
- Remove src/vb-aliases.h and include/libvbucket.h

Change-Id: I762c68a9501e8b27313594c88b58b8683a06ca46
Reviewed-on: http://review.couchbase.org/37398
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>