pgsql: Remove traces of BeOS.

Remove traces of BeOS.

Commit 15abc7788e6 tolerated namespace pollution from BeOS system
headers. Commit 44f902122 de-supported BeOS. Since that stuff didn't
make it into the Meson build system, synchronize by removing from
configure.

Author: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Reviewed-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Reviewed-by: Japin Li <japinli(at)hotmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> (the idea, not the patch)
Discussion: https://postgr.es/m/ME3P282MB3166F9D1F71F787929C0C7E7B6312%40ME3P282MB3166.AUSP282.PROD.OUTLOOK.COM

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a2d9a9b95ad933853dd18894393615d37257f43b

Modified Files
--------------
configure | 44 --------------------------
configure.ac | 5 ---
src/include/c.h | 12 -------
src/include/pg_config.h.in | 12 -------
src/interfaces/ecpg/include/ecpg_config.h.in | 3 --
src/interfaces/ecpg/include/meson.build | 1 -
src/interfaces/ecpg/include/pgtypes_interval.h | 4 ---
7 files changed, 81 deletions(-)