xds: use slices.Equal to simplify code

[jishudashu]

In the Go 1.21 standard library, a new function has been introduced that enhances code conciseness and readability. It can be find here.

RELEASE NOTES: N/A

[linux-foundation-easycla]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.30%. Comparing base (8adcc94) to head (f289336).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8472      +/-   ##
==========================================
- Coverage   82.31%   82.30%   -0.02%     
==========================================
  Files         414      413       -1     
  Lines       40464    40513      +49     
==========================================
+ Hits        33308    33344      +36     
- Misses       5791     5798       +7     
- Partials     1365     1371       +6     

Files with missing lines	Coverage Δ
xds/internal/balancer/clusterimpl/clusterimpl.go	91.28% <100.00%> (+1.04%)	⬆️
xds/internal/balancer/clusterimpl/config.go	100.00% <ø> (ø)

... and 28 files with indirect coverage changes

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[jishudashu]

• ❌ - login: @jishudashu . The commit (12e0f59) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

Signed.

[arjan-bal]

LGTM, adding a second reviewer.