pgsql: Remove large fill factor support from dynahash.c.

Remove large fill factor support from dynahash.c.

Since ancient times we have had support for a fill factor (maximum load
factor) to be set for a dynahash hash table, but:

1. It was an integer, whereas for in-memory hash tables interesting
load factor targets are probably somewhere near the 0.75-1.0 range.

2. It was implemented in a way that performed an expensive division
operation that regularly showed up in profiles.

3. We are not aware of anyone ever having used a non-default value.

Therefore, remove support, effectively fixing it at 1.

Author: Jakub Wartak <Jakub(dot)Wartak(at)tomtom(dot)com>
Reviewed-by: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Reviewed-by: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Reviewed-by: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Reviewed-by: David Rowley <dgrowleyml(at)gmail(dot)com>
Discussion: https://postgr.es/m/VI1PR0701MB696044FC35013A96FECC7AC8F62D0%40VI1PR0701MB6960.eurprd07.prod.outlook.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/be0a6666656ec3f68eb7d8e7abab5139fcd47012

Modified Files
--------------
src/backend/utils/hash/dynahash.c | 20 ++++++--------------
src/include/utils/hsearch.h | 2 --
2 files changed, 6 insertions(+), 16 deletions(-)