pgsql: Cleanup useless assignments and checks

Cleanup useless assignments and checks

This cleans up a couple of areas:
- Remove XLogSegNo calculation for the last WAL segment in backup in
xlog.c (7d70809 has moved this logic entirely to xlogbackup.c when
building the contents of the backup history file).
- Remove check on log_min_duration in analyze.c, as it is already true
where this code path is reached.
- Simplify call to find_option() in guc.c.

Author: Ranier Vilela
Reviewed-by: Masahiko Sawada
Discussion: https://postgr.es/m/CAEudQArCDQQiPiFR16=yu9k5s2tp4tgEe1U1ZbkW4ofx81AWWQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c42cd05c586235fa9e84fb4a3682286cf551df0e

Modified Files
--------------
src/backend/access/transam/xlog.c | 1 -
src/backend/commands/analyze.c    | 3 +--
src/backend/utils/misc/guc.c      | 4 +---
3 files changed, 2 insertions(+), 6 deletions(-)