cluster: remove deprecated return value

[xenowits]

Remove isLegacyLock bool return value when loading cluster from either manifest or lock file.

category: refactor
ticket: none

[codecov]

Codecov Report

Patch coverage: 60.00% and project coverage change: -0.04 ⚠️

Comparison is base (faf48c8) 53.43% compared to head (ddf26eb) 53.39%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2407      +/-   ##
==========================================
- Coverage   53.43%   53.39%   -0.04%     
==========================================
  Files         196      196              
  Lines       26282    26281       -1     
==========================================
- Hits        14044    14034      -10     
- Misses      10497    10506       +9     
  Partials     1741     1741              

Impacted Files	Coverage Δ
app/disk.go	0.00% <0.00%> (ø)
cmd/addvalidators.go	51.94% <57.14%> (-0.15%)	⬇️
cluster/manifest/load.go	50.00% <66.66%> (ø)
cmd/combine/combine.go	67.24% <100.00%> (ø)

... and 11 files with indirect coverage changes

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