CharacterizeImageTask no longer copies the mask

CharacterizeImageTask was making a copy of the mask and restoring
restoring it for each iteration of the "characterize" method.
This was unnecessary because the code that sets the mask planes
in question clears the planes before setting them again.

python/lsst/pipe/tasks/characterizeImage.py

@@ -343,9 +343,6 @@ def characterize(self, exposure, exposureIdInfo, background=None):
         if background is None:
             background = BackgroundList()
 
-        # make a deep copy of the mask
-        originalMask = exposure.getMaskedImage().getMask().clone()
-
         # subtract an initial estimate of background level
         estBg = estimateBackground(
             exposure = exposure,
@@ -358,11 +355,6 @@ def characterize(self, exposure, exposureIdInfo, background=None):
 
         psfIterations = self.config.psfIterations if self.config.doMeasurePsf else 1
         for i in range(psfIterations):
-            if i > 1:
-                # restore original mask so that detections and cosmic rays
-                # are only marked by the final iteration
-                exposure.getMaskedImage().getMask()[:] = originalMask
-
             dmeRes = self.detectMeasureAndEstimatePsf(
                 exposure = exposure,
                 exposureIdInfo = exposureIdInfo,