Simplify build-system further

Remove Fragile from the list of dependencies

It is not necessary for building 'gio' anymore,
since the upgrade to 'glib v2_58'.

Remove "online" and "reset_lock" Meson-options

Building Squeekboard should work offline.

Use a single "Cargo.toml"-file instead of splitting it into parts

and putting it back together when building.

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/623>

meson_options.txt

@@ -11,14 +11,6 @@ option('find_orphans',
        type: 'boolean', value: false,
        description: 'Check if all present layout files are included in resources.')
 
-option('online',
-       type: 'boolean', value: true,
-       description: 'Pull packages from the internet while building, as opposed to a local registry.')
-       
-option('reset_lock',
-       type: 'boolean', value: false,
-       description: 'Resets Cargo.lock to the one found in the source repo. Does not affect builds with online == false.')
-
 option('strict',
        type: 'boolean', value: true,
        description: 'Turn more warnings into errors')