pgsql: Make lsn argument of walrcv_create_slot() optional

Make lsn argument of walrcv_create_slot() optional

Some callers are not using it, so it's wasteful to have to specify it.

Reviewed-by: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/CA+fd4k4BcYrYucNfTnK-CQX3+jsG+PRPEhHAUSo-W4P0Lec57A@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c67a55da4ea0caa18547fd1533110e9126ba8d47

Modified Files
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src/backend/commands/subscriptioncmds.c                     | 3 +--
src/backend/replication/libpqwalreceiver/libpqwalreceiver.c | 6 ++++--
2 files changed, 5 insertions(+), 4 deletions(-)