[Fixes #10040] Remove auto-generated thumbnail for documents

[marthamareal]

References #10040 ## Checklist

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• [x] There is a ticket in https://github.com/GeoNode/geonode/issues describing the issue/improvement/feature (a notable exemption is, changes not visible to end-users)
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• [ ] Commits adding new texts do use gettext and have updated .po / .mo files (without location infos)

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[lgtm-com[bot]]

This pull request introduces 1 alert when merging 4ecb1dbb306bac27fb1852c80ce7795d1a3aa55d into 540024f1b1ca2b42e16e7da3b71f85128b8052b4 - view on LGTM.com

new alerts:

• 1 for Unreachable code

[codecov[bot]]

Codecov Report

Merging #10045 (cda7db8) into master (540024f) will increase coverage by 0.00%. The diff coverage is 77.77%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #10045   +/-   ##
=======================================
  Coverage   61.45%   61.45%           
=======================================
  Files         823      824    +1     
  Lines       50533    50510   -23     
  Branches     7767     7760    -7     
=======================================
- Hits        31055    31041   -14     
+ Misses      17796    17794    -2     
+ Partials     1682     1675    -7