meson: Remove --debug from mkosi arguments

The exit status issue for which we introduced this was fixed so
let's remove --debug again to make the meson output less verbose.

meson.build

@@ -2619,7 +2619,6 @@ if mkosi.found()
                         '--cache-dir', meson.current_build_dir() / 'mkosi.cache',
                         '--build-dir', meson.current_build_dir() / 'mkosi.builddir',
                         '--force',
-                        '--debug',
                         'build',
                 ],
                 depends : mkosi_depends,

test/integration-test-wrapper.py

@@ -81,7 +81,6 @@ def main():
 
     cmd = [
         'mkosi',
-        '--debug',
         '--directory', os.fspath(args.meson_source_dir),
         '--output-dir', os.fspath(args.meson_build_dir / 'mkosi.output'),
         '--extra-search-path', os.fspath(args.meson_build_dir),