Remove isapprox for intervals which has been moved to IntervalSets

[daanhb]

It seems the tests failed due to an isapprox check. Since isapprox moved, perhaps we can also remove the test from DomainSets, tag a new release, and worry about the error being thrown elsewhere?

[dlfivefifty]

OK agreed

[codecov[bot]]

Codecov Report

Base: 86.09% // Head: 86.09% // Decreases project coverage by -0.00% :warning:

Coverage data is based on head (65fefcc) compared to base (8bce5e6). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #123 +/- ## ========================================== - Coverage 86.09% 86.09% -0.01% ========================================== Files 31 31 Lines 2496 2495 -1 ========================================== - Hits 2149 2148 -1 Misses 347 347 ``` | [Impacted Files](https://codecov.io/gh/JuliaApproximation/DomainSets.jl/pull/123?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation) | Coverage Δ | | |---|---|---| | [src/domains/interval.jl](https://codecov.io/gh/JuliaApproximation/DomainSets.jl/pull/123/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL2RvbWFpbnMvaW50ZXJ2YWwuamw=) | `94.62% <ø> (-0.03%)` | :arrow_down: | 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=JuliaApproximation). 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=JuliaApproximation)

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