[widgets] Delete parameter.py and corresponding tests

These were accidentally checked in and are superseded
by parameterwidget.py and its corresponding tests.
4 jobs for 215_parameter_widget in 10 minutes and 2 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #166117
docker-build
build_linux_36

00:06:13

passed #166118
macosx
build_macosx_36

00:09:46

failed #166115
docker-build
build_linux_36

00:15:19

failed #166116
macosx
build_macosx_36

00:15:20