Revert "refactor: Clear pre-edit buffer before commit"

[kanru]

This reverts commit b0f7685.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 53.14%. Comparing base (9eed0c2) to head (19e1770).
Report is 4 commits behind head on master.

Files	Patch %	Lines
src/ibus-chewing-engine.c	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #228   +/-   ##
=======================================
  Coverage   53.14%   53.14%           
=======================================
  Files          17       17           
  Lines        2081     2081           
=======================================
  Hits         1106     1106           
  Misses        975      975           

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