pgsql: Put all the prototypes for hashfn.c into the same header file.

Put all the prototypes for hashfn.c into the same header file.

Previously, some of the prototypes for functions in hashfn.c were
in utils/hashutils.h and others were in utils/hsearch.h, but that
is confusing and has no particular benefit.

Patch by me, reviewed by Suraj Kharage and Mark Dilger.

Discussion: http://postgr.es/m/CA+TgmoaRiG4TXND8QuM6JXFRkM_1wL2ZNhzaUKsuec9-4yrkgw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9341c783cc42ffae5860c86bdc713bd47d734ffd

Modified Files
--------------
src/backend/lib/dshash.c          |  2 +-
src/backend/utils/hash/dynahash.c |  1 +
src/include/utils/hashutils.h     |  6 ++++++
src/include/utils/hsearch.h       | 17 ++++-------------
4 files changed, 12 insertions(+), 14 deletions(-)