Remove logical_read_local_xlog_page

Remove logical_read_local_xlog_page

It devolved into a content-less wrapper over read_local_xlog_page, with
nothing to add, plus it's easily confused with walsender's
logical_read_xlog_page.  There doesn't seem to be any reason for it to
stay.

src/include/replication/logicalfuncs.h becomes empty, so remove it too.
The prototypes it initially had were absorbed by generated fmgrprotos.h.

Discussion: https://postgr.es/m/20191115214102[email protected]