Have methods take AChannelManager as Deref::Target

[tnull]

In #2535, we had lightning-invoice use the AChannelManager trait to clean up the trait boundaries.

While we now gave it as a &C, we can relax that requirement further and instead have C: Deref targetting AChannelManager.

[codecov-commenter]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (6016101) 89.03% compared to head (808e72a) 90.07%.
Report is 80 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2652      +/-   ##
==========================================
+ Coverage   89.03%   90.07%   +1.03%     
==========================================
  Files         112      112              
  Lines       86351    94845    +8494     
  Branches    86351    94845    +8494     
==========================================
+ Hits        76879    85427    +8548     
+ Misses       7235     7131     -104     
- Partials     2237     2287      +50     

Files	Coverage Δ
lightning-invoice/src/payment.rs	77.48% <66.66%> (+0.17%)	⬆️

... and 37 files with indirect coverage changes

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