pkg/proc: remove callFrameRegs from stackIterator
pkg/proc: remove callFrameRegs from stackIterator

Since it's just a scratchpad to calculate the new set of registers it
makes more sense to have it as a local variable in Next and
advanceRegs.

aarzilli/delve,dlsniper/delve,go-delve/delve,dlsniper/delve,dr2chase/delve,alexbrainman/delve,dr2chase/delve,go-delve/delve,aarzilli/delve,go-delve/delve,alexbrainman/delve,dlsniper/delve,dr2chase/delve,derekparker/delve,alexbrainman/delve,aarzilli/delve,go-delve/delve,derekparker/delve,go-delve/delve,aarzilli/delve,derekparker/delve