cov: empty coverage overlay (#2119)

The overlay depended on the version number, which caused errors when upgrading.

Also update cabal description.

postgrest.cabal

@@ -2,7 +2,7 @@ name:               postgrest
 version:            9.0.0.20220107
 synopsis:           REST API for any Postgres database
 description:        Reads the schema of a PostgreSQL database and creates RESTful routes
-                    for the tables and views, supporting all HTTP verbs that security
+                    for tables, views, and functions, supporting all HTTP verbs that security
                     permits.
 license:            MIT
 license-file:       LICENSE

test/coverage.overlay

@@ -1,5 +0,0 @@
-module "postgrest-9.0.0.20211220-inplace/PostgREST.Middleware" {
-  inside "corsPolicy" {
-    tick "[]" on line 133;
-  }
-}