Remove libpq.rc, use win32ver.rc for libpq

Remove libpq.rc, use win32ver.rc for libpq

For historical reasons, libpq used a separate libpq.rc file for the
Windows builds while all other components use a common file
win32ver.rc.  With a bit of tweaking, the libpq build can also use the
win32ver.rc file.  This removes a bit of duplicative code.

Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/ad505e61-a923-e114-9f38-9867d161073f@2ndquadrant.com