Remove as_Universe (Issue #2920)

[IAlibay]

Fixes #2920

Changes made in this Pull Request:

• Removes as_Universe from MDAnalysis.core.universe
• :class:MDAnalysis.analysis.leaflet.LeafletFinder no longer accepts paths to files for the universe argument.

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

[pep8speaks]

Hello @IAlibay! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file package/MDAnalysis/__init__.py:

Line 205:1: E402 module level import not at top of file

Comment last updated at 2020-08-27 13:21:23 UTC

[lilyminium]

Looks good! Weird that there were no tests for as_Universe.

[IAlibay]

Looks good! Weird that there were no tests for as_Universe.

Yeah it looks like it was only covered indirectly via LeafletFinder (that or I missed something and I'm going to wake up to Travis complaining 🤷‍♂️ )

[lilyminium]

    def test_as_Universe():

>       assert mda.as_Universe is mda.core.universe.as_Universe

E       AttributeError: module 'MDAnalysis' has no attribute 'as_Universe'

Oops, grepped in the wrong folder. There is a test...

Approved w/o due diligence

[lilyminium]

Please remove test :-)

[codecov]

Codecov Report

Merging #2922 into develop will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #2922      +/-   ##
===========================================
+ Coverage    92.96%   93.00%   +0.03%     
===========================================
  Files          187      187              
  Lines        24935    24928       -7     
  Branches      3258     3250       -8     
===========================================
+ Hits         23182    23184       +2     
+ Misses        1705     1696       -9     
  Partials        48       48              

Impacted Files	Coverage Δ
package/MDAnalysis/analysis/leaflet.py	96.29% <ø> (-0.05%)	⬇️
package/MDAnalysis/core/universe.py	97.88% <ø> (+0.43%)	⬆️
package/MDAnalysis/__init__.py	91.89% <100.00%> (ø)
package/MDAnalysis/coordinates/base.py	95.12% <0.00%> (+0.48%)	⬆️
package/MDAnalysis/due.py	75.00% <0.00%> (+8.33%)	⬆️

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