ci: remove cross compilation step of cloud build job

[MarlonGamez]

Related: #6348

Description
This PR removes the cross target dependency from the release target, as well as the uploading to our gcs bucket. These things are now handled in our kokoro jobs and no longer need to be done here.

Follow-up Work (remove if N/A)
Move over the rest of our jobs to kokoro (release-lts, latest builds)

[aaron-prindle]

LGTM

[codecov]

Codecov Report

Merging #6956 (3ac0760) into main (290280e) will decrease coverage by 1.66%.
The diff coverage is 56.70%.

@@            Coverage Diff             @@
##             main    #6956      +/-   ##
==========================================
- Coverage   70.48%   68.81%   -1.67%     
==========================================
  Files         515      551      +36     
  Lines       23150    25296    +2146     
==========================================
+ Hits        16317    17408    +1091     
- Misses       5776     6716     +940     
- Partials     1057     1172     +115     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/deploy.go	52.00% <ø> (-1.85%)	⬇️
cmd/skaffold/app/cmd/dev.go	84.61% <0.00%> (ø)
cmd/skaffold/app/cmd/render.go	36.66% <0.00%> (-4.72%)	⬇️
cmd/skaffold/skaffold.go	0.00% <0.00%> (ø)
cmd/skaffold/app/cmd/inspect_tests.go	62.50% <14.28%> (-1.14%)	⬇️
cmd/skaffold/app/cmd/lsp.go	28.12% <28.12%> (ø)
cmd/skaffold/app/cmd/fix.go	68.85% <40.00%> (-7.62%)	⬇️
cmd/skaffold/app/cmd/lint.go	42.85% <42.85%> (ø)
cmd/skaffold/app/cmd/find_configs.go	48.88% <50.00%> (+0.24%)	⬆️
cmd/skaffold/app/skaffold.go	76.19% <70.00%> (-8.43%)	⬇️
... and 170 more

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