Remove tile_for_point SQL functions

This removes both the pl/pgsql version and the shared library version
of the `tile_for_point` SQL function. This function was only used in some
old migrations, and is not required for production usage.

Removing this function simplifies the installation and configuration for
new developers.

These SQL functions are separate from the `tile_for_point` ruby/C function
which is part of the quad_tile gem. This function is still used when
creating and updating database records.

Fixes #3110.

docker/postgres/Dockerfile

@@ -1,7 +1,4 @@
 FROM postgres:11
 
-# Add db init script to install OSM-specific Postgres functions/extensions.
+# Add db init script to install OSM-specific Postgres user.
 ADD docker/postgres/openstreetmap-postgres-init.sh /docker-entrypoint-initdb.d/
-
-# Custom database functions are in a SQL file.
-ADD db/functions/functions.sql /usr/local/share/osm-db-functions.sql

docker/postgres/openstreetmap-postgres-init.sh

@@ -7,6 +7,3 @@ psql -v ON_ERROR_STOP=1 -U "$POSTGRES_USER" <<-EOSQL
     CREATE USER openstreetmap SUPERUSER PASSWORD 'openstreetmap';
     GRANT ALL PRIVILEGES ON DATABASE openstreetmap TO openstreetmap;
 EOSQL
-
-# Define custom functions
-psql -v ON_ERROR_STOP=1 -U "$POSTGRES_USER" -f "/usr/local/share/osm-db-functions.sql" openstreetmap