Simplify progress report during scanning

We now get less progress feedback, but in exchange, our progress job is
simpler. Previously, our progress bar would often get wonky towards the
end of the scan and I didn't have the energy to debug that.

Besides, people don't care about that level of progress feedback.

core/engine.py

@@ -449,7 +449,7 @@ class Group:
             return self[0]
 
 
-def get_groups(matches, j=job.nulljob):
+def get_groups(matches):
     """Returns a list of :class:`Group` from ``matches``.
 
     Create groups out of match pairs in the smartest way possible.
@@ -458,7 +458,7 @@ def get_groups(matches, j=job.nulljob):
     dupe2group = {}
     groups = []
     try:
-        for match in j.iter_with_progress(matches, tr("Grouped %d/%d matches"), JOB_REFRESH_RATE):
+        for match in matches:
             first, second, _ = match
             first_group = dupe2group.get(first)
             second_group = dupe2group.get(second)