Delete legacy.go for lockup module

[mattverse]

Closes: #XXX

Description

Per conversation in #804 to re-delete legacy.go

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

[codecov-commenter]

Codecov Report

Merging #879 (6a178a1) into main (bdff1da) will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #879      +/-   ##
==========================================
+ Coverage   20.21%   20.30%   +0.09%     
==========================================
  Files         192      191       -1     
  Lines       24854    24740     -114     
==========================================
  Hits         5023     5023              
+ Misses      18907    18793     -114     
  Partials      924      924              

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[ValarDragon]

TY!