Change aggregate functions to use new syntax

[robe]

For this, it's not necessary to drop existing (so no need to put in a Changed: …). Internally PostgreSQL shows the new syntax anyway.

Just to keep our code base more up to date and make it easier to stuff args such as parallel = safe without having to rewrite the display.

Note that most of our postgis aggs look like old syntax:

CREATE AGGREGATE some_agg( basetype = geometry ... )

But the newer syntax has been supported since at least PostgreSQL 8.4

CREATE AGGREGATE some_agg(geometry)( ... )

​https://www.postgresql.org/docs/8.4/static/sql-createaggregate.html

So we can certainly use in 2.1+

​https://www.postgresql.org/docs/8.4/static/sql-createaggregate.html

[robe]

did this already as part of marking all as parallel safe.