Split the plpython regression test into test cases arranged by topic, instead

of the previous monolithic setup-create-run sequence, that was apparently
inherited from a previous test infrastructure, but makes working with the
tests and adding new ones weird.

src/pl/plpython/sql/plpython_schema.sql

@@ -39,10 +39,6 @@ CREATE TABLE xsequences (
 	) ;
 CREATE INDEX xsequences_pid_idx ON xsequences(pid) ;
 
-CREATE TABLE unicode_test (
-	testvalue  text NOT NULL
-);
-
 CREATE TABLE table_record (
 	first text,
 	second int4