pgsql: Document pg_dump(all) --no-security-label instead of --security-

Document pg_dump(all) --no-security-label instead of --security-label.

The former is the option actually supported by these commands.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=a1b0035949da09bb0f19d2d9c2d54ca54ca55752

Modified Files
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doc/src/sgml/ref/pg_dump.sgml | 5 ++---
doc/src/sgml/ref/pg_dumpall.sgml | 5 ++---
2 files changed, 4 insertions(+), 6 deletions(-)