sql/swh-func: Move hash_sha1 function to the func namespace

sql/swh-func.sql

+-- Postgresql index helper function
+create or replace function hash_sha1(text)
+    returns text
+    language sql strict immutable
+as $$
+    select encode(digest($1, 'sha1'), 'hex')
+$$;
+
+comment on function hash_sha1(text) is 'Compute sha1 hash as text';
+
 -- create a temporary table with a single "bytea" column for fast object lookup.
 create or replace function swh_mktemp_bytea()
     returns void

sql/swh-init.sql

@@ -2,12 +2,3 @@ create extension if not exists btree_gist;
 create extension if not exists pgcrypto;
 
 create or replace language plpgsql;
-
-create or replace function hash_sha1(text)
-    returns text
-    language sql strict immutable
-as $$
-    select encode(digest($1, 'sha1'), 'hex')
-$$;
-
-comment on function hash_sha1(text) is 'Compute sha1 hash as text';