drop dynamic client wrappers in namespaced informers

[dprotaso]

Follow up of #2742

I didn't realize these were manual created - so deleting the code manually.

Part of #2739

[dprotaso]

/assign @pierDipi

[codecov]

Codecov Report

Patch coverage: 83.78% and no project coverage change.

Comparison is base (300df43) 81.53% compared to head (b2576ff) 81.54%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2744   +/-   ##
=======================================
  Coverage   81.53%   81.54%           
=======================================
  Files         163      163           
  Lines       10018    10055   +37     
=======================================
+ Hits         8168     8199   +31     
- Misses       1606     1610    +4     
- Partials      244      246    +2     

Impacted Files	Coverage Δ
apis/duck/v1/source_types.go	48.64% <ø> (ø)
apis/duck/v1beta1/destination.go	94.17% <83.33%> (-2.30%)	⬇️
apis/duck/v1/destination.go	94.23% <84.21%> (-5.77%)	⬇️

... and 2 files with indirect coverage changes

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[xtreme-vikram-yadav]

/lgtm

[knative-prow]

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