Remove unused and failing import of contextmanagers

I think this Import just got in there by mistake.  It doesn't work on Windows or Linux, and it doesn't seem to be used.  ?

Traceback (most recent call last):
  File "__main__.py", line 23, in <module>
  File "roam\mainwindow.pyc", line 40, in <module>
    QLabel {
  File "roam\dataentrywidget.pyc", line 11, in <module>
    
  File "roam\editorwidgets\featureformwidget.pyc", line 9, in <module>
    
  File "roam\api\__init__.pyc", line 5, in <module>
    
  File "roam\api\featureform.pyc", line 37, in <module>
  File "roam\api\utils.pyc", line 5, in <module>
    
ImportError: cannot import name contextmanager