cdsbalancer: Remove UpdateAddresses handling

[arjan-bal]

Following the dual-stack changes that established pick_first as the universal leaf policy and the subsequent removal of the legacy pick_first implementation, ClientConn.UpdateAddresses is no longer utilized within the xDS LB policy tree. When addresses change, old SubConns are now shut down and new ones are created.

This PR makes UpdateAddresses a no-op.

RELEASE NOTES: N/A

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.40%. Comparing base (900ffa9) to head (118a850).

Files with missing lines	Patch %	Lines
internal/xds/balancer/cdsbalancer/cdsbalancer.go	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8811      +/-   ##
==========================================
+ Coverage   83.25%   83.40%   +0.14%     
==========================================
  Files         417      417              
  Lines       32978    32976       -2     
==========================================
+ Hits        27457    27503      +46     
+ Misses       4106     4074      -32     
+ Partials     1415     1399      -16     

Files with missing lines	Coverage Δ
internal/xds/balancer/cdsbalancer/cdsbalancer.go	86.25% <50.00%> (+0.93%)	⬆️

... and 18 files with indirect coverage changes

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[easwars]

@eshitachandwani : Please consider yourself as the primary reviewer of this PR. And loop me in once you have approved it. Thanks.