introspection: Include channel state in output

[prashantv]

We'll need to exclude channel state from the pre/post state verification
since the channel state is expected to change.

Remove an unused function, all verification is now part of testutils.

[codecov]

Codecov Report

Merging #692 into dev will increase coverage by 0.4%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##              dev     #692     +/-   ##
=========================================
+ Coverage   86.72%   87.13%   +0.4%     
=========================================
  Files          40       40             
  Lines        4023     4026      +3     
=========================================
+ Hits         3489     3508     +19     
+ Misses        402      394      -8     
+ Partials      132      124      -8

Impacted Files	Coverage Δ
introspection.go	92.38% <100%> (-3.28%)	⬇️
mex.go	72.09% <0%> (-2.8%)	⬇️
peer.go	93.45% <0%> (-0.37%)	⬇️
outbound.go	86.2% <0%> (+1.14%)	⬆️
inbound.go	81.05% <0%> (+1.57%)	⬆️
connection.go	85.64% <0%> (+6.29%)	⬆️

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