[FIX] Remove unused code

[eric-haibin-lin]

Description

Remove an unused line of code

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

[mli]

Job PR-528/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-528/1/index.html

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@b05c2f8). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #528   +/-   ##
=========================================
  Coverage          ?   70.04%           
=========================================
  Files             ?      122           
  Lines             ?    10462           
  Branches          ?        0           
=========================================
  Hits              ?     7328           
  Misses            ?     3134           
  Partials          ?        0

Flag	Coverage Δ
#PR528	70.04% <ø> (?)
#notserial	46.64% <ø> (?)
#py2	69.76% <ø> (?)
#py3	69.9% <ø> (?)
#serial	54.68% <ø> (?)

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@b05c2f8). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #528   +/-   ##
=========================================
  Coverage          ?   70.04%           
=========================================
  Files             ?      122           
  Lines             ?    10462           
  Branches          ?        0           
=========================================
  Hits              ?     7328           
  Misses            ?     3134           
  Partials          ?        0

Flag	Coverage Δ
#PR528	70.04% <ø> (?)
#notserial	46.64% <ø> (?)
#py2	69.76% <ø> (?)
#py3	69.9% <ø> (?)
#serial	54.68% <ø> (?)