Fix failure to commit RecADCOnlyUnit.dfm

When I made the recadc_interface branch, and specifically the change
to make the "Record AD Signals Only" checkbox persistent, I forgot
to commit the .dfm file.  (Since I subsequently never bothered moving
that file back from the repo to the WinFluor workstation, this error
was not noticed until now, following the upgrade to 3.4.5.)