chore: remove error return in IterateConsensusStateAscending

[damiannolan]

Description

• Removing error return from IterateConsensusStateAscending
• Updating legacy code
• Updating tests

closes: #1886

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov-commenter]

Codecov Report

Merging #1896 (8da542f) into updated-02-client-refactor (81f2d09) will increase coverage by 0.05%.
The diff coverage is 66.66%.

@@                      Coverage Diff                       @@
##           updated-02-client-refactor    #1896      +/-   ##
==============================================================
+ Coverage                       80.02%   80.08%   +0.05%     
==============================================================
  Files                             167      167              
  Lines                           11759    11753       -6     
==============================================================
+ Hits                             9410     9412       +2     
+ Misses                           1931     1925       -6     
+ Partials                          418      416       -2     

Impacted Files	Coverage Δ
modules/light-clients/07-tendermint/store.go	79.21% <50.00%> (+1.07%)	⬆️
modules/core/02-client/legacy/v100/store.go	75.96% <100.00%> (+2.37%)	⬆️
modules/light-clients/07-tendermint/update.go	89.82% <100.00%> (+1.26%)	⬆️

[colin-axner]

LGTM, thanks! Should we add a changelog?