cli/registry/client: remove dependency on trust / notary

[thaJeztah]

• follow-up to Assorted cleanups to reduce trust / notary imports #5878

The client was only using the Actions consts, but the trust package also has a dependency on notary. Remove the import to prevent Notary becoming a dependency for uses of the cli code.

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Looks like I forgot to include this one in #5878 - this one should also be trivial; the predefined vars are nice, but don't add much value, and we shouldn't depend on the trust code for this (more likely it should've been the other way round)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 59.31%. Comparing base (076ec3b) to head (e3da0cc).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5880   +/-   ##
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  Coverage   59.31%   59.31%           
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  Files         353      353           
  Lines       29735    29735           
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  Hits        17637    17637           
  Misses      11117    11117           
  Partials      981      981