pgsql: Clean up ICU includes.

Clean up ICU includes.

Remove ICU includes from pg_locale.h, and instead include them in the
few C files that need ICU. Clean up a few other includes in passing.

Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/48911db71d953edec66df0d2ce303563d631fbe0.camel@j-davis.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/af2d4ca191a4552217eceace21fde6ebc2b85770

Modified Files
--------------
src/backend/commands/collationcmds.c  |  4 ++++
src/backend/utils/adt/formatting.c    |  8 --------
src/backend/utils/adt/pg_locale.c     | 14 ++++++++++++++
src/backend/utils/adt/pg_locale_icu.c |  2 ++
src/backend/utils/adt/varlena.c       | 11 ++++++-----
src/include/utils/pg_locale.h         | 16 ++++------------
6 files changed, 30 insertions(+), 25 deletions(-)