fingerprint-dialog: Disconnect signals and reset stages on enroll-restart

This happens if going to the previous page when enrolling a finger
11 jobs for async-fprint-query-3-36 in 2 minutes and 56 seconds (queued for 10 seconds)
Status Job ID Name Coverage
  Build
passed #747799
build

00:01:49

 
  Test
passed #747800
test

00:01:06

 
  Manual
manual #747806
allowed to fail manual
armv8
manual #747802
allowed to fail manual
asan
manual #747801
allowed to fail manual
flatpak
manual #747805
allowed to fail manual
msan
manual #747807
allowed to fail manual
ppc64le
manual #747803
allowed to fail manual
tsan
manual #747804
allowed to fail manual
ubsan
 
  Review
manual #747808
allowed to fail manual
review
manual #747809
allowed to fail manual
stop_review