chore: remove handling of node versions 8, 9 and 10 in tests

[SimenB]

Which problem is this PR solving?

Extracted from #3689.

Fixes # N/A

Short description of the changes

CI only runs on Node 14+, so this is dead code

Type of change

Housekeeping

How Has This Been Tested?

CI

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

Merging #3696 (b25db6e) into main (dbe005f) will decrease coverage by 0.05%.
The diff coverage is 75.00%.

❗ Current head b25db6e differs from pull request most recent head a7992d0. Consider uploading reports for the commit a7992d0 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3696      +/-   ##
==========================================
- Coverage   93.70%   93.65%   -0.05%     
==========================================
  Files         277      277              
  Lines        8446     8462      +16     
  Branches     1753     1756       +3     
==========================================
+ Hits         7914     7925      +11     
- Misses        532      537       +5     

Impacted Files	Coverage Δ
...tal/packages/otlp-transformer/src/metrics/types.ts	100.00% <ø> (ø)
packages/sdk-metrics/src/view/Aggregation.ts	93.82% <55.55%> (-4.79%)	⬇️
.../packages/otlp-transformer/src/metrics/internal.ts	98.00% <100.00%> (+0.27%)	⬆️
packages/sdk-metrics/src/aggregator/index.ts	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[SimenB]

weird that CI is failing here but green on main - I haven't changed the failing files

[Flarna]

similar fails seen in #3699