lsyscache: free IndexAmRoutine objects returned by GetIndexAmRoutineByAmId()

Hi Hackers,

I noticed this problem while reviewing Tom’s patch [1]. In lsyscache.c,
there are multiple places that get IndexAmRoutine
by GetIndexAmRoutineByAmId(). Only one function get_opmethod_canorder()
pfree the returned object, while the other 3
functions get_op_index_interpretation(), equality_ops_are_compatible()
and comparison_ops_are_compatible() all call GetIndexAmRoutineByAmId() in
for loops but without freeing the memory.

While these paths are not hot enough to cause leaks that matter in
practice, I think for consistency, we should free the memory.

[1] https://postgr.es/m/2380165.1766871097@sss.pgh.pa.us

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/