Bug 26634: [20.05.x] Remove GetHoldRule subroutine in C4::Reserves

Bug 26634: [20.05.x] Remove GetHoldRule subroutine in C4::Reserves

This routine is only used internally and incorrectly overrides
the precedence of holds rules - it should be removed

This patch removes the routine, adjusts tests, and adds test to
confirm correct precedence is followed

To test:
1 - At the All Libraries level, create a circ rule for a specific patron category and a specific item type that only allows 1 hold
2 - At the branch-specific level for Branch A, create an All/All rule that allows 2 holds
3 - confirm ReservesControll is set to patron's library
4 - find a patron from Branch A of the category for which you made your rule
5 - find two bibs with items of the itype got which you made your rule
6 - place a hold on one bib. success!
7 - try to place a hold on the second bib. you're told you cannot because the patron is only allowed 1 hold
8 - apply patch, restart services
9 - try to place your second hold again, success!

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>