do not index links in core repository (#1202)

Author: tomkralidis

etc/migrations/2.x-3.0/migrate.sql

@@ -6,4 +6,5 @@ alter table records add column themes TEXT;
 alter table records add column illuminationelevationangle TEXT;
 alter table records alter column cloudcover type real using cast(cloudcover as float);
 alter table records alter column distancevalue type real using cast(distancevalue as float);
+drop index ix_records_links;
 vacuum;

pycsw/core/repository.py

@@ -903,7 +903,7 @@ def setup(database, table, create_sfsql_tables=True, postgis_geometry_column='wk
 
         # distribution
         # links: JSON list of dicts with properties: name, description, protocol, url
-        Column('links', Text, index=True),
+        Column('links', Text, index=False),
         # contacts: JSON list of dicts with owslib contact properties, name, organization, email, role, etc.
         Column('contacts', Text, index=True),
     )