Make expect_payment_failed_conditions a function

[TheBlueMatt]

This reduces macro generated code in tests a good bit, and moves us
one step further away from using macros everywhere when we don't
need to.

Did this in an earlier version of #1495 but didn't need it, figured it was still worth upstreaming.

[codecov-commenter]

Codecov Report

Merging #1496 (4671a08) into main (8e5cf75) will increase coverage by 0.60%.
The diff coverage is 93.54%.

❗ Current head 4671a08 differs from pull request most recent head 70acdf9. Consider uploading reports for the commit 70acdf9 to get more accurate results

@@            Coverage Diff             @@
##             main    #1496      +/-   ##
==========================================
+ Coverage   90.93%   91.53%   +0.60%     
==========================================
  Files          80       80              
  Lines       43386    48432    +5046     
  Branches    43386    48432    +5046     
==========================================
+ Hits        39451    44331    +4880     
- Misses       3935     4101     +166     

Impacted Files	Coverage Δ
lightning/src/ln/functional_test_utils.rs	96.08% <91.30%> (+0.66%)	⬆️
lightning/src/ln/functional_tests.rs	97.34% <100.00%> (+0.11%)	⬆️
lightning/src/ln/onion_route_tests.rs	97.51% <100.00%> (ø)
lightning/src/ln/payment_tests.rs	99.24% <100.00%> (-0.01%)	⬇️
lightning/src/ln/priv_short_conf_tests.rs	96.60% <100.00%> (ø)
lightning/src/util/events.rs	40.18% <0.00%> (-1.81%)	⬇️
lightning/src/chain/onchaintx.rs	93.98% <0.00%> (-0.93%)	⬇️
lightning/src/ln/reorg_tests.rs	100.00% <0.00%> (ø)
... and 12 more

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[arik-so]

go, go, go, go, go!

[tnull]

Needs a rebase it seems, other than that LGTM!

[TheBlueMatt]

Rebased and fixed a nonsense variable name introduced when this commit wasn't intended for upstream.

[tnull]

LGTM, feel free to squash to fix the failing check_commits test.

[TheBlueMatt]

Squashed without changes, should be good to go:

$ git diff-tree -U5 4671a088 70acdf93
$