Remove PARTIAL_LINKING?

Hi,

We've still some support for building the backend with PARTIAL_LINKING /
SUBSYS.o instead of the current objfiles.txt approach.
http://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=9956ddc19164b02dc1925fb389a1af77472eba5e

Any objections to removing that? Seems that's largely just removing a
bit of logic from common.mk.

Note I'm not talking about whatever that aix logic in src/backend is,
that seems independent except for sharing the SUBSYS.o name.

I just encountered this while polishing my JIT patch, which has
*optional* support for building inlinable version of backend
functions. It'd not be hard to make it work for PARTIAL_LINKING, but I
kinda don't see the point 10 years later...

Greetings,

Andres Freund