desktop_common: drop inert Flatpak GTK_THEME override

The task wrote /etc/flatpak/overrides/global, but Flatpak reads its
overrides from /var/lib/flatpak/overrides/, so the file was never
honored. The dark theme is now correctly applied to Flatpak apps via
xdg-desktop-portal (color-scheme + gtk-theme), which works as long as
the portal backends can start — fixed in the prior commit.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ansible/roles/profile_desktop_common/tasks/main.yml

@@ -464,28 +464,6 @@
     - (desktop_flatpak_extensions | default([])) | length > 0
     - item | length > 0
 
-- name: Ensure /etc/flatpak/overrides exists
-  tags: [packages, flatpak, theme]
-  ansible.builtin.file:
-    path: /etc/flatpak/overrides
-    state: directory
-    owner: root
-    group: root
-    mode: "0755"
-  when: (desktop_flatpak_packages | default([])) | length > 0
-
-- name: Force dark GTK theme for Flatpak applications
-  tags: [packages, flatpak, theme]
-  ansible.builtin.copy:
-    dest: /etc/flatpak/overrides/global
-    content: |
-      [Environment]
-      GTK_THEME={{ desktop_flatpak_gtk_theme | default('Yaru-Blue-dark') }}
-    owner: root
-    group: root
-    mode: "0644"
-  when: (desktop_flatpak_packages | default([])) | length > 0
-
 - name: Bootstrap rustup toolchain installer
   tags: [packages]
   block: