Remove deprecated defined API

[mantoni]

Purpose (TL;DR) - mandatory

The assert.defined and refute.defined APIs have been deprecated in favor of assert.isUndefined and refute.isUndefined to be in line with other APIs like isNull. This change removes defined from the API.

Ref #89 #93

How to verify - mandatory

1. Check out this branch
2. npm install
3. npm t

Checklist for author

• npm run lint passes
• References to standard library functions are cached.

[coveralls]

Pull Request Test Coverage Report for Build 319

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 315:	0.0%
Covered Lines:	654
Relevant Lines:	654

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💛 - Coveralls

[mantoni]

Duplicated in line 122.