Make all VLDB interactions use VLF/VLSF names

src/volser/volser.p.h defined the values used in VLDB entries.  These values
appear (by exhaustive walk of source and by inspection of the volser's rxrpc
api) to be unused by any aspect of the volser and were solely used in
communication with the VLDB.

This patch deletes the misplaced definitions and moves the entire tree to
use the VLF_{RW,RO,BACK}EXISTS and VLSF_* macros from vlserver/vldbint.xg .
No include wrangling was needed; these definitions have always been in scope
but relatively unused.

It also serves to head off a potential problem, which actually motivated the
whole thing: ITSRWREPL was 0x10, which was claimed as VLSF_UUID;
VLSF_RWREPLICA is 0x40, which did not have an ITS equivalent.  As ITSRWREPL
was not used, this had never shown itself in operation.  There was no ITS
semantic equivalent of VLSF_UUID.

Change-Id: I60426c2635976b9ac34bf820a8aec7a0c8575e20
Reviewed-on: http://gerrit.openafs.org/11331
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>