pgsql: Remove dead code

Remove dead code

As of commit 9895b35cb88, AlterDomainAddConstraint() can only be
called with constraints of type CONSTR_CHECK and CONSTR_NOTNULL.  So
all the code to check for and reject other constraint type values is
dead and can be removed.

Author: jian he <jian.universality@gmail.com>
Discussion:
https://www.postgresql.org/message-id/flat/CACJufxHitd5LGLBSSAPShhtDWxT0ViVKTHinkYW-skBX93TcpA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7407b2d48cf37bc8847ae6c47dde2164ef2faa34

Modified Files
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src/backend/commands/typecmds.c | 54 ++---------------------------------------
1 file changed, 2 insertions(+), 52 deletions(-)