Remove obsolete prompt displayed when generating Partial Volumes

[amymmorton]

depreciated.

Please remove ui popup when partial volume button click

[jcfr]

The prompt was originally introduced through #108, @amymmorton do you know in which pull request the dialog became obsolete ?

[amymmorton]

The #121 was the new direction- but we are still unable to progess successfully

(the functionality in this issue was part of projective VRG generation. The analysis of this accuracy was performed internally again #110 The resultant 2d-3d results for first metacarpal and trapezium were poor and the usability in 4dct prompted us to go the 3d-3d route)