pgsql: Do not allow removal of superuser privileges from bootstrap user

Do not allow removal of superuser privileges from bootstrap user.

A bootstrap user who is not a superuser will still own many
important system objects, such as the pg_catalog schema, that
will likely allow that user to regain superuser status. Therefore,
allowing the superuser property to be removed from the superuser
creates a false perception of security where none exists.

Although removing superuser from the bootstrap user is also a bad idea
and should be considered unsupported in all released versions, no
back-patch, as this is a behavior change.

Discussion: http://postgr.es/m/CA+TgmoZirCwArJms_fgvLBFrC6b=HdxmG7iAhv+kt_=NBA7tEw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e530be2c5ce77475d56ccf8f4e0c4872b666ad5f

Modified Files
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src/backend/commands/user.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)