o/snapstate: do not restart again for snapd along the undo path inside undoUnlinkCurrentSnap

[Meulengracht]

Actually we skip the entire link code for snapd as this has already been done in undoLinkSnap. Add a wait for restart/reboot in undoRemoveAlias

REF: SNAPDENG-34315

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 78.22%. Comparing base (24a0034) to head (c4521ae).
Report is 96 commits behind head on master.

Files with missing lines	Patch %	Lines
overlord/snapstate/handlers.go	40.00%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #14917      +/-   ##
==========================================
+ Coverage   78.20%   78.22%   +0.01%     
==========================================
  Files        1151     1158       +7     
  Lines      151396   152955    +1559     
==========================================
+ Hits       118402   119643    +1241     
- Misses      25662    25921     +259     
- Partials     7332     7391      +59     

Flag	Coverage Δ
unittests	78.22% <40.00%> (+0.01%)	⬆️

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