vtorc: skip unnecessary backend read in logic.LockShard(...)

[timvaillancourt]

Description

This PR removes a backend read of the vitess_tablet sqlite3 table in VTOrc during a logic.LockShard(...)

This backend read is only getting the keyspace and shard name, which is already known (and now passed) by the caller of LockShard(...)

Related Issue(s)

#17330

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.

Project coverage is 67.51%. Comparing base (41a8d1d) to head (a72340f).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtorc/logic/tablet_discovery.go	0.00%	7 Missing ⚠️
go/vt/vtorc/logic/topology_recovery.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #17900   +/-   ##
=======================================
  Coverage   67.50%   67.51%           
=======================================
  Files        1595     1595           
  Lines      259640   259671   +31     
=======================================
+ Hits       175280   175313   +33     
+ Misses      84360    84358    -2     

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