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

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 
Reviewed-by: Alvaro Herrera 
Reviewed-by: Tomas Vondra 
Reviewed-by: Thomas Munro 
Reviewed-by: David Rowley 
Discussion: https://postgr.es/m/VI1PR0701MB696044FC35013A96FECC7AC8F62D0%40VI1PR0701MB6960.eurprd07.prod.outlook.com

Branch
------
master

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

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