[widgets][plottereditor] Remove test specific method

It was not needed at all.
2 jobs for plottereditor_remove_test_specific_method in 11 minutes and 13 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #169352
docker-build
build_linux_36

00:11:11

passed #169353
macosx
build_macosx_36

00:10:47