pg_dump/nls.mk is missing a file

Hello.

Upon reviewing my translation, I discovered that filter.c was not
included in the nls.mk of pg_dump. Additional it appears that two '.h'
files have been included for a long time, but they seem unnecessary as
their removal does not affect the results. The attached patch is
intended to correct these issues.

For Meson, on the other hand, I believe there is nothing in particular
that needs to be done.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center