fix: don't set the HTTP referer header

[midgleyc]

Spun out of https://kolmafia.us/threads/getting-an-error-unable-to-log-in.27387/#post-167382

On earlier versions of Java 11 this isn't valid to do, and does no harm
to omit.

Remove code dealing with pics.communityofloathing.com, which no longer
resolves.

[codecov]

Codecov Report

Merging #661 (c091aff) into main (40fd12a) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main     #661      +/-   ##
============================================
- Coverage     21.85%   21.84%   -0.01%     
+ Complexity     9411     9407       -4     
============================================
  Files          1003     1003              
  Lines        157154   157146       -8     
  Branches      34831    34829       -2     
============================================
- Hits          34339    34330       -9     
  Misses       116553   116553              
- Partials       6262     6263       +1     

Impacted Files	Coverage Δ
.../sourceforge/kolmafia/utilities/FileUtilities.java	29.31% <ø> (+0.29%)	⬆️
...t/sourceforge/kolmafia/request/GenericRequest.java	21.41% <100.00%> (-0.11%)	⬇️
...rceforge/kolmafia/persistence/HolidayDatabase.java	34.57% <0.00%> (-1.17%)	⬇️
...forge/kolmafia/persistence/ConcoctionDatabase.java	43.48% <0.00%> (-0.06%)	⬇️

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