doc: Fix SQL keywords lists

Some keywords were listed as both reserved and nonreserved.  Fix as
appropriate.

doc/src/sgml/keywords/sql2016-02-reserved.txt

@@ -189,7 +189,6 @@ MATCH_NUMBER
 MATCH_RECOGNIZE
 MATCHES
 MAX
-MEASURES
 MEMBER
 MERGE
 METHOD
@@ -240,7 +239,6 @@ PERCENT_RANK
 PERCENTILE_CONT
 PERCENTILE_DISC
 PERIOD
-PERMUTE
 PORTION
 POSITION
 POSITION_REGEX
@@ -342,7 +340,6 @@ UESCAPE
 UNION
 UNIQUE
 UNKNOWN
-UNMATCHED
 UNNEST
 UPDATE
 UPPER