[dart-dio-next] Removes dioLibrary option

[josh-burton]

As there is no longer a fork of the dio library this option can be removed
#10305

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@jaumard @josh-burton @amondnet @sbu-WBT @kuhnroyal @agilob @ahmednfwela

[wing328]

The Dart 2.1.0 tests failed: https://github.com/OpenAPITools/openapi-generator/runs/4415838129?check_suite_focus=true

Can you please take a look when you've time?

[ahmednfwela]

@wing328 looks like a typical maven timeout

[wing328]

Yup, I restarted it but no luck. Will give it another try tomorrow.

[wing328]

@josh-burton can you please resolve the merge conflicts when you've time? Then I'll merge. Thanks.