refactor(instrumentation-grpc): clean up remnants of 'grpc' package instrumentation

[pichlermarc]

Which problem is this PR solving?

We had some unused code left over from back when @opentelemetry/instrumentation-grpc still supported the grpc package (now only @grpc/gprc-js is supported). This PR gets rid of the wrapper that used to make two instrumentation look like one.

Fixes #4201

Type of change

• refactor

How Has This Been Tested?

• Tested locally on a typescript project without @grpc/grpc-js to ensure we don't rely on @grpc/grpc-js types in the public interface

[codecov]

Codecov Report

Merging #4420 (4aec62e) into main (efa6307) will increase coverage by 0.04%.
The diff coverage is 92.22%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4420      +/-   ##
==========================================
+ Coverage   92.37%   92.41%   +0.04%     
==========================================
  Files         331      330       -1     
  Lines        9518     9497      -21     
  Branches     2021     2021              
==========================================
- Hits         8792     8777      -15     
+ Misses        726      720       -6     

Files	Coverage Δ
...ntelemetry-instrumentation-grpc/src/clientUtils.ts	96.70% <100.00%> (ø)
...ntelemetry-instrumentation-grpc/src/serverUtils.ts	91.78% <100.00%> (ø)
...emetry-instrumentation-grpc/src/instrumentation.ts	92.09% <92.04%> (+19.36%)	⬆️

[Flarna]

Seems it's mostly a code move/adaption to move.
I haven't looked into each and every line.