pgsql: doc: Remove unused ids

doc: Remove unused ids

Some reference pages contained id attributes on refname elements.
These were apparently copied around from ancient times, but they don't
serve a purpose.  FOP issues minor warnings about them.  So it's
easiest to just remove them.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/7e39b968f118c6444bd3a3bd59c3e9d73e652e0c

Modified Files
--------------
doc/src/sgml/ref/clusterdb.sgml  | 2 +-
doc/src/sgml/ref/postmaster.sgml | 2 +-
doc/src/sgml/ref/reindexdb.sgml  | 2 +-
doc/src/sgml/ref/vacuumdb.sgml   | 2 +-
4 files changed, 4 insertions(+), 4 deletions(-)