Cleanup sockrw functions/decl

- Use lcbconn_* prefix like the rest
- Hide functions which are not used outside of readwrite.c
- Normalize naming (We use E/C instead of the older "V0" and "V1")
- Simply Completion-Mode enter. The onread/onwrite functions have been
  replace by a simple lcb_Crb_enter() function

Change-Id: I83780bab4a4f60d8fd78b6b5e6dad47c5f673534
Reviewed-on: http://review.couchbase.org/33604
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>