pg_basebackup: Remove short option -k
-k meant --no-verify-checksums, which is the opposite of what initdb
uses -k for. After discussion, a short option does not seem necessary,
so just keep the long option.
Discussion: https://www.postgresql.org/message-id/flat/
d510f8aa-19e1-d06e-7630-
ad27f7441d68%402ndquadrant.com