chore(kuma-cp) remove Envoy V2 leftovers

[jakubdyszkiewicz]

Summary

Remove xds utils for Envoy V2 and some V2 leftovers around the code, so we can upgrade Go Control Plane

Issues resolved

No issue

Documentation

• No docs

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

Backwards compatibility

• It it backwards compatible, V2 is long gone.

[codecov-commenter]

Codecov Report

Merging #2686 (3c1a80c) into master (14b527b) will increase coverage by 0.23%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2686      +/-   ##
==========================================
+ Coverage   51.96%   52.20%   +0.23%     
==========================================
  Files         871      864       -7     
  Lines       49505    49181     -324     
==========================================
- Hits        25727    25676      -51     
+ Misses      21698    21421     -277     
- Partials     2080     2084       +4     

Impacted Files	Coverage Δ
pkg/config/xds/bootstrap/config.go	56.75% <ø> (ø)
...ore/resources/apis/mesh/proxytemplate_validator.go	96.87% <100.00%> (ø)
pkg/core/xds/resource.go	83.75% <100.00%> (-0.96%)	⬇️
app/kumactl/cmd/root.go	70.17% <0.00%> (-3.51%)	⬇️
pkg/core/bootstrap/autoconfig.go	54.46% <0.00%> (+8.03%)	⬆️

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