feat: do not use legacy grpc loadObject

[alexander-fenster]

Finally, loadPackageDefinition just works for both grpc versions we have.

• Tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

[codecov]

Codecov Report

Merging #477 into master will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #477      +/-   ##
==========================================
+ Coverage   82.83%   82.95%   +0.12%     
==========================================
  Files          50       50              
  Lines        3198     3192       -6     
  Branches       82       81       -1     
==========================================
- Hits         2649     2648       -1     
+ Misses        536      532       -4     
+ Partials       13       12       -1

Impacted Files	Coverage Δ
src/grpc.ts	88.88% <ø> (+4.51%)	⬆️

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[bcoe]

LGTM, deleting code is the best.