pgsql: Remove precedence hacks no longer needed without postfix operato

Remove precedence hacks no longer needed without postfix operators.

It's no longer necessary to assign explicit precedences to GENERATED,
NULL_P, PRESERVE, or STRIP_P.

Actually, we don't need to assign precedence to IDENT either; that was
really just there to govern the behavior of target_el's "a_expr IDENT"
production, which no longer ends with that terminal.  However, it seems
like a good idea to continue to do so, because it provides a reference
point for a precedence level that we can assign to other unreserved
keywords that lack a natural precedence level.

Research by Peter Eisentraut and John Naylor; comment rewrite by me.

Discussion: https://postgr.es/m/38ca86db-42ab-9b48-2902-337a0d6b8311@2ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/28a61fc6c58fbfb83e416411f55e7d6ec47279ff

Modified Files
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src/backend/parser/gram.y | 34 +++++++++++++++-------------------
1 file changed, 15 insertions(+), 19 deletions(-)