simplify UpdateClient proposal

[colin-axner]

Description

closes: #176

---

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 #181 (6f10f18) into main (4570955) will increase coverage by 0.04%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main     #181      +/-   ##
==========================================
+ Coverage   80.04%   80.08%   +0.04%     
==========================================
  Files         109      109              
  Lines        6481     6474       -7     
==========================================
- Hits         5188     5185       -3     
+ Misses        936      932       -4     
  Partials      357      357              

Impacted Files	Coverage Δ
modules/core/02-client/types/proposal.go	83.92% <ø> (-0.82%)	⬇️
...ht-clients/06-solomachine/types/proposal_handle.go	100.00% <ø> (ø)
...s/light-clients/09-localhost/types/client_state.go	93.91% <ø> (ø)
...ght-clients/07-tendermint/types/proposal_handle.go	85.00% <64.70%> (+4.23%)	⬆️
modules/core/02-client/keeper/proposal.go	92.15% <100.00%> (+1.04%)	⬆️
modules/light-clients/07-tendermint/types/store.go	87.82% <100.00%> (+0.21%)	⬆️

[lgtm-com]

This pull request introduces 1 alert when merging 05d7e67 into f412334 - view on LGTM.com

new alerts:

• 1 for Useless assignment to local variable