fix(plugin-chart-echarts): remove columns from formData

[villebro]

🐛 Bug Fix
Make sure columns property isn't defined in formData, as it is a reserved parameter with a specific meaning in QueryObject.

[vercel]

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[rusackas]

Oh man... LGTM! Let me know if you need help carrying it across to Superset.

[codecov]

Codecov Report

Merging #901 (47f48f2) into master (2d87d6f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #901   +/-   ##
=======================================
  Coverage   26.66%   26.66%           
=======================================
  Files         405      405           
  Lines        8258     8258           
  Branches     1127     1127           
=======================================
  Hits         2202     2202           
  Misses       5927     5927           
  Partials      129      129           

Impacted Files	Coverage Δ
...ins/plugin-chart-echarts/src/BoxPlot/buildQuery.ts	43.75% <ø> (ø)

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[ktmud]

How about this change: https://github.com/apache-superset/superset-ui/pull/889/files#diff-68ae7687936cc7b2de6790b6c6abb9b48a150dc9977b665b3717a7e3f4a90632 ?

[ktmud]

This change is good, but it may need to be updated soon after I deprecate groupby in #889