lint: Fix lint errors in config/

[algochoi]

Summary

Running golangci-lint run config/ (removing the commit hash gate in golangci.yml) generates the following lint error:

config/consensus.go:682:12: S1033: unnecessary guard around call to delete (gosimple)
                                } else if _, has := cParam.ApprovedUpgrades[consensusVersion]; has {
config/migrate.go:131:5: SA4003: no value of type uint32 is less than 0 (staticcheck)
        if version < 0 {

This PR fixes this lint error by removing the guard around the delete call (the code is functionally the same, since deleting nil map key/value is a no op) and removing the negative check for uint values.

Test Plan

[codecov]

Codecov Report

Merging #5416 (91c8fb4) into master (1abbd50) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master    #5416   +/-   ##
=======================================
  Coverage   55.40%   55.40%           
=======================================
  Files         452      452           
  Lines       63855    63853    -2     
=======================================
- Hits        35379    35378    -1     
- Misses      26044    26046    +2     
+ Partials     2432     2429    -3     

Impacted Files	Coverage Δ
config/consensus.go	86.19% <0.00%> (ø)
config/migrate.go	78.46% <ø> (+1.18%)	⬆️

... and 7 files with indirect coverage changes

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[tzaffi]

LGTM