[netinstall] Repair schema IDs

The schema is considered invalid by **some** versions of
configvalidator (or rather, the underlying jsonschema):

```
128: '#definitions/groups' does not match '^[^#]*#?$'
128:
128: Failed validating 'pattern' in metaschema['properties']['definitions']['additionalProperties']['$dynamicRef']['allOf'][0]['properties']['$id']:
128:     {'$comment': 'Non-empty fragments not allowed.',
128:      '$ref': '#/$defs/uriReferenceString',
128:      'pattern': '^[^#]*#?$'}
```

Remove the `#` from the IDs.

src/modules/netinstall/netinstall.schema.yaml

@@ -6,7 +6,7 @@ $schema: https://json-schema.org/draft-07/schema#
 $id: https://calamares.io/schemas/netinstall
 definitions:
     package:
-        $id: '#definitions/package'
+        $id: 'definitions/package'
         oneOf:
         -
             type: string
@@ -20,7 +20,7 @@ definitions:
                 name: { type: string }
                 description: { type: string }
     group:
-        $id: '#definitions/group'
+        $id: 'definitions/group'
         type: object
         description: Longer discussion in `netinstall.conf` file under 'Groups Format'
         properties:
@@ -28,7 +28,7 @@ definitions:
             description: { type: string }
             packages:
                 type: array
-                items: { $ref: '#definitions/package' }
+                items: { $ref: 'definitions/package' }
             hidden: { type: boolean, default: false }
             selected: { type: boolean }
             critical: { type: boolean, default: false }
@@ -36,7 +36,7 @@ definitions:
             expanded: { type: boolean }
             subgroups:
                 type: array
-                items: { $ref: '#definitions/group' }
+                items: { $ref: 'definitions/group' }
             pre-install:
                 type: string
                 description: an optional command to run within the new system before the group's
@@ -56,9 +56,9 @@ definitions:
             required: [name, description, packages] # bottom-most (sub)group requires some package (otherwise, why bother?)
     # This should validate `netinstall.yaml` also.
     groups:
-        $id: '#definitions/groups'
+        $id: 'definitions/groups'
         type: array
-        items: { $ref: '#definitions/group' }
+        items: { $ref: 'definitions/group' }
 
 oneOf:
 -   # netinstall.conf
@@ -74,16 +74,16 @@ oneOf:
             properties:
                 sidebar: { type: string }
                 title: { type: string }
-        groups: { $ref: '#definitions/groups' }
+        groups: { $ref: 'definitions/groups' }
     required: [ groupsUrl ]
-    
+
 -   # Groups file with top level *groups* key
     type: object
     description: Groups file with top level *groups* key
     additionalProperties: false
     properties:
-        groups: { $ref: '#definitions/groups' }
+        groups: { $ref: 'definitions/groups' }
     required: [ groups ]
-    
+
 -   # Groups file bare
-    { $ref: '#definitions/groups' }
+    { $ref: 'definitions/groups' }