Remove dead settings

[int-y1]

trafficstars

DEFAULT_SELECT2_*: Tested by visiting /admin/judge/problem/1/change/. Version 4.0.3 (May 2016) still works, so there is no need to upgrade.

JUDGE_AMQP_PATH: Dead according to git log -G JUDGE_AMQP_PATH.

[Xyene]

Could you please squash your commits, or relabel them meaningfully? Otherwise LGTM.

[codecov-commenter]

Codecov Report

Merging #1952 (806d2cc) into master (8faf2bf) will decrease coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1952      +/-   ##
==========================================
- Coverage   46.51%   46.49%   -0.02%     
==========================================
  Files         236      236              
  Lines       13085    13082       -3     
==========================================
- Hits         6086     6083       -3     
  Misses       6999     6999              

Impacted Files	Coverage Δ
judge/widgets/select2.py	55.68% <ø> (-0.99%)	:arrow_down:
dmoj/settings.py	97.67% <100.00%> (-0.02%)	:arrow_down:

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