[users] Fix up schema syntax

- Remove schema items *availableShells* and *avatarFilePath* because
  those have no implementation.

src/modules/users/users.conf

@@ -124,7 +124,7 @@ allowWeakPasswordsDefault: false
 #    and rely on a correct configuration file in /etc/default/useradd
 #  - set, non-empty, use that path as shell. No validation is done
 #    that the shell actually exists or is executable.
-# userShell: /bin/bash
+userShell: /bin/bash
 
 # Hostname setting
 #

src/modules/users/users.schema.yaml

@@ -4,15 +4,15 @@ $id: https://calamares.io/schemas/users
 additionalProperties: false
 type: object
 properties:
-    "defaultGroups":
-        required: true
-        type: seq
-        sequence:
-            - { type: str }
-    "autologinGroup": { type: string, required: true }
-    "doAutologin": { type: boolean, default: true }
-    "sudoersGroup": { type: string, required: true }
-    "setRootPassword": { type: boolean, default: true }
-    "availableShells": { type: str }
-    "avatarFilePath": { type: str }
-    "doReusePassword": { type: boolean, default: true }
+    defaultGroups:
+        type: array
+        items: { type: string }
+    autologinGroup: { type: string }
+    doAutologin: { type: boolean, default: true }
+    sudoersGroup: { type: string }
+    setRootPassword: { type: boolean, default: true }
+    doReusePassword: { type: boolean, default: true }
+required:
+    - defaultGroups
+    - autologinGroup
+    - sudoersGroup