Remove unused type annotation

[codecov[bot]]

Codecov Report

Base: 78.46% // Head: 78.46% // No change to project coverage :thumbsup:

Coverage data is based on head (97c158b) compared to base (5ba05a6). Patch coverage: 66.66% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #261 +/- ## ======================================= Coverage 78.46% 78.46% ======================================= Files 36 36 Lines 1788 1788 ======================================= Hits 1403 1403 Misses 385 385 ``` | [Impacted Files](https://codecov.io/gh/jump-dev/SumOfSquares.jl/pull/261?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jump-dev) | Coverage Δ | | |---|---|---| | [src/constraint.jl](https://codecov.io/gh/jump-dev/SumOfSquares.jl/pull/261/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jump-dev#diff-c3JjL2NvbnN0cmFpbnQuamw=) | `75.21% <0.00%> (ø)` | | | [src/Certificate/Certificate.jl](https://codecov.io/gh/jump-dev/SumOfSquares.jl/pull/261/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jump-dev#diff-c3JjL0NlcnRpZmljYXRlL0NlcnRpZmljYXRlLmps) | `98.71% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jump-dev). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jump-dev)

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