tox.ini: remove additionally missed mock deps

[blueyed]

Ref: #4415 (comment)

Found by @asottile.

[codecov]

Codecov Report

Merging #4417 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4417   +/-   ##
=======================================
  Coverage   95.89%   95.89%           
=======================================
  Files         111      111           
  Lines       25008    25008           
  Branches     2438     2438           
=======================================
  Hits        23982    23982           
  Misses        724      724           
  Partials      302      302

Flag	Coverage Δ
#docs	30.17% <ø> (+0.07%)	⬆️
#doctesting	30.17% <ø> (+0.07%)	⬆️
#linting	30.17% <ø> (+0.07%)	⬆️
#linux	95.72% <ø> (ø)	⬆️
#nobyte	92.65% <ø> (ø)	⬆️
#numpy	93.42% <ø> (-0.02%)	⬇️
#pexpect	41.87% <ø> (-0.03%)	⬇️
#py27	94.02% <ø> (+0.01%)	⬆️
#py34	92.16% <ø> (+0.06%)	⬆️
#py35	92.18% <ø> (+0.06%)	⬆️
#py36	92.2% <ø> (+0.06%)	⬆️
#py37	94.1% <ø> (ø)	⬆️
#trial	93.42% <ø> (-0.02%)	⬇️
#windows	94.1% <ø> (ø)	⬆️
#xdist	93.95% <ø> (ø)	⬆️

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