Remove PF_USED_FOR_ASSERTS_ONLY from variables in general use

Remove PF_USED_FOR_ASSERTS_ONLY from variables in general use

fsstate in process_pending_requests (in postgres_fdw.c) was added in
8998e3cafa2 as an assertion-only variable,  1ec7fca8592 stated using
the variable outside of assertions.

rd_index in get_index_column_opclass (in lsyscache.c) was introduced
in 2a6368343ff, and then promptly used in the fix commit 7e041603904
shortly thereafter.

This removes the PG_USED_FOR_ASSERTS_ONLY variable decoration from
the above mentioned variables.

Reviewed-by: Greg Nancarrow <gregn4422@gmail.com>
Discussion: https://postgr.es/m/F959106C-0F21-43A5-B2AE-D007D51ACBEE@yesql.se