Fix #2123: Remove unnecessary calls to getParentFragment() to avoid NPE

[domdomegg]

Description (required)

Fixes #2123 Crashes viewing media in explore mode

What changes did you make and why?

Removed unnecessary getParentFragment() calls. I'm not sure why it is used here given getActivity() should already go up the chain until it reaches the calling activity or returns null.

Tests performed (required)

All automated tests pass.

Tested 2.9.0-debug-hotfix-explore-media-detail~7b5e1068 on Galaxy Nexus (emulator) with API level 28.
Tested 2.9.0-debug-hotfix-explore-media-detail~7b5e1068 on Samsung Galax S6 with API level 25.

[codecov-io]

Codecov Report

Merging #2138 into master will not change coverage.
The diff coverage is 0%.

@@          Coverage Diff           @@
##           master   #2138   +/-   ##
======================================
  Coverage    5.52%   5.52%           
======================================
  Files         234     234           
  Lines       11596   11596           
  Branches     1079    1079           
======================================
  Hits          641     641           
  Misses      10902   10902           
  Partials       53      53

Impacted Files	Coverage Δ
...ee/nrw/commons/media/MediaDetailPagerFragment.java	0% <0%> (ø)	⬆️

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[neslihanturan]

Thanks @domdomegg , works as expected.