remove timestamp check from solomachine misbehaviour

[colin-axner]

Description

closes: #7824

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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

[cwgoes]

ACK

[codecov]

Codecov Report

Merging #7915 (3d966c4) into master (f3e4964) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7915      +/-   ##
==========================================
- Coverage   54.18%   54.18%   -0.01%     
==========================================
  Files         612      612              
  Lines       38989    38987       -2     
==========================================
- Hits        21126    21124       -2     
  Misses      15696    15696              
  Partials     2167     2167