shell: Remove the lock button from the shell

Only the date time panel used it, all other panels add their own shell using
cc_shell_embed_widget_in_header which was added after the date time panel was
written. Update the date time panel to use this method.
11 jobs for no-shared-lock-button in 5 minutes and 18 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #127764
build

00:02:00

 
  Test
passed #127766
asan

00:03:18

passed #127765
test

00:00:36

 
  Manual
manual #127771
allowed to fail manual
armv8
manual #127767
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flatpak
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msan
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ppc64le
manual #127768
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tsan
manual #127769
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ubsan
 
  Review
manual #127773
allowed to fail manual
review
manual #127774
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