pgsql: Remove explicit superuser checks in favor of ACLs

Remove explicit superuser checks in favor of ACLs

This removes the explicit superuser checks in the various file-access
functions in the backend, specifically pg_ls_dir(), pg_read_file(),
pg_read_binary_file(), and pg_stat_file(). Instead, EXECUTE is REVOKE'd
from public for these, meaning that only a superuser is able to run them
by default, but access to them can be GRANT'd to other roles.

Reviewed-By: Michael Paquier
Discussion: https://postgr.es/m/20171231191939.GR2416%40tamriel.snowman.net

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e79350fef2917522571add750e3e21af293b50fe

Modified Files
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src/backend/catalog/system_views.sql | 14 ++++++++++++++
src/backend/utils/adt/genfile.c | 20 --------------------
2 files changed, 14 insertions(+), 20 deletions(-)