Revert "StepWaveformクラスにoverrideキーワードを追加"

This reverts commit a119b9efe469b700ec9be92d8de1d9bde2c822fe.
Revert "BasicWaveformのクラス群にoverrideキーワードを追加"

This reverts commit 99895fabc815e9fa35fc46aa9bd1bb1edac6d3a7.