doc pg_constraint.convalidated column description need update

hi.

catalog.sgml:

<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>convalidated</structfield> <type>bool</type>
</para>
<para>
Has the constraint been validated?
Currently, can be false only for foreign keys and CHECK constraints
</para></entry>
</row>

with NOT NULL NOT VALID,
we need rephrase it to something like:
"Currently, can be false only for foreign keys, CHECK and not-null constraints"
I am also ok with just deleting it.

BTW, I happen to notice a minor issue:
some pg_catalog table column entry descriptions ending with a period,
some didn't.