ftplugin: do not duplicate jedi_usages autocommands

[blueyed]

Fixes #882.

[codecov-io]

Codecov Report

Merging #883 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #883   +/-   ##
=======================================
  Coverage   55.73%   55.73%           
=======================================
  Files           3        3           
  Lines         619      619           
  Branches      122      122           
=======================================
  Hits          345      345           
  Misses        242      242           
  Partials       32       32

Flag	Coverage Δ
#py27	54.6% <ø> (ø)	⬆️
#py36	53.47% <ø> (ø)	⬆️

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[liushapku]

Thanks for fixing this. When will it get merged?

[blueyed]

Now! \o/
Forgot about it apparently.

[liushapku]

Thanks!