Remove installation of schema_triggers

Schema triggers dependency was deprecated time ago. See
5d43faecaf/NEWS.md (0120-2016-01-27)

client/test/expected/00_installation_test.out

@@ -1,6 +1,5 @@
 -- Install dependencies
 CREATE EXTENSION postgis;
-CREATE EXTENSION schema_triggers;
 CREATE EXTENSION plpythonu;
 CREATE EXTENSION cartodb;
 CREATE EXTENSION plproxy;

client/test/sql/00_installation_test.sql

@@ -1,6 +1,5 @@
 -- Install dependencies
 CREATE EXTENSION postgis;
-CREATE EXTENSION schema_triggers;
 CREATE EXTENSION plpythonu;
 CREATE EXTENSION cartodb;
 CREATE EXTENSION plproxy;