pgsql: Remove fallback declaration for tas().

Remove fallback declaration for tas().

The last definition of tas() in s_lock.c was removed in commit
718aa43a4e, and the last tas.s file was removed in commit
25f36066dd, so this is dead code.

Reviewed-by: Tristan Partin <tristan(at)partin(dot)io>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reviewed-by: Kirill Reshke <reshkekirill(at)gmail(dot)com>
Discussion: https://postgr.es/m/afkUeI7UhacZ5ZFm%40nathan

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2079be3311b1d0a717d70404a9b9492ec06cc3e2

Modified Files
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src/backend/Makefile | 2 +-
src/backend/port/.gitignore | 1 -
src/backend/port/meson.build | 2 +-
src/backend/port/tas/dummy.s | 0
src/include/storage/s_lock.h | 7 -------
5 files changed, 2 insertions(+), 10 deletions(-)