Remove flaky tests.

[jkmarx]

Resolves #2610

[scottx611x]

Looking a second time we have good test coverage for dataset deletion https://github.com/refinery-platform/refinery-platform/blob/develop/refinery/core/tests.py#L1665-L1727 & https://github.com/refinery-platform/refinery-platform/blob/develop/refinery/core/tests.py#L610 and analysis deletion https://github.com/refinery-platform/refinery-platform/blob/develop/refinery/core/tests.py#L859-L874 & https://github.com/refinery-platform/refinery-platform/blob/develop/refinery/core/tests.py#L2011-L2073 So maybe these Selenium Tests were/are a bit overkill. If you're feeling up to it we could remove all of these Selenium-based ones related to ui deletion

[codecov]

Codecov Report

Merging #2613 into develop will decrease coverage by 0.73%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop    #2613      +/-   ##
===========================================
- Coverage    55.33%   54.59%   -0.74%     
===========================================
  Files          399      398       -1     
  Lines        25922    25553     -369     
  Branches      1245     1240       -5     
===========================================
- Hits         14343    13950     -393     
- Misses       11579    11603      +24

Impacted Files	Coverage Δ
refinery/selenium_testing/utils.py	90.9% <ø> (+9.89%)	⬆️
refinery/user_files_manager/tests.py	100% <100%> (ø)	⬆️
refinery/factory_boy/utils.py	86.95% <0%> (-13.05%)	⬇️
...ry/core/management/commands/create_public_group.py	80% <0%> (-4%)	⬇️
refinery/core/api.py	41.36% <0%> (-2.58%)	⬇️
refinery/core/models.py	69.92% <0%> (-2.07%)	⬇️
refinery/data_set_manager/search_indexes.py	96.55% <0%> (-1.3%)	⬇️
refinery/core/utils.py	35.81% <0%> (-0.36%)	⬇️
refinery/core/views.py	26.93% <0%> (-0.21%)	⬇️
refinery/data_set_manager/tests.py	99.76% <0%> (-0.04%)	⬇️
... and 2 more

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