pgsql: Make VM clear take a RelFileLocator and not fake relcache

Make VM clear take a RelFileLocator and not fake relcache

This brings it in line with visibilitymap_set(). An upcoming commit will
start reading visibility map buffers with XLogReadBuffer*() functions,
so we no longer require a relation object to pin the visibility map,
allowing us to remove this fake relcache business altogether.

While we're at it, remove a spurious const qualifier from the
RelFileLocator parameter to visibilitymap_set().

Author: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Discussion: https://postgr.es/m/flat/CAAKRu_bn%2Be7F4yPFBgFbnP%2BsyJRKyNK092bjD2LKvZW7O4Svag%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2340fb8f02b28d2fe7f0023d84c3055a38cd5b9e

Modified Files
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contrib/pg_surgery/heap_surgery.c | 2 +-
src/backend/access/heap/heapam.c | 16 ++++++++--------
src/backend/access/heap/heapam_xlog.c | 14 +++++++-------
src/backend/access/heap/pruneheap.c | 2 +-
src/backend/access/heap/visibilitymap.c | 9 ++++++---
src/include/access/visibilitymap.h | 4 ++--
6 files changed, 25 insertions(+), 22 deletions(-)