TEST-73-LOCALE: do not unnecessarily restart systemd-localed

TEST-73-LOCALE: do not unnecessarily restart systemd-localed

It is not necessary to clear previous keymap assignment, as
`localectl set-keymap` will anyway overwrite the previous assignment.

This drops the unnecessary restart of systemd-localed in the loop.
The mkosi test image contains about 500~700 keymaps. The test
performance is greatly improved by reducing the number of restarts,
especially when the test is running with sanitizers.

On Fedora 41 with sanitizers,
Before:
1/1 systemd:integration-tests / TEST-73-LOCALE OK             1157.50s
After:
1/1 systemd:integration-tests / TEST-73-LOCALE OK              104.43s