simplemerge: delete unused exception class `CantReprocessAndShowBase`

The only user was removed in f18830651811 (simplemerge: burn "minimal"
feature to the ground, 2014-08-05).

Differential Revision: https://phab.mercurial-scm.org/D11998

mercurial/simplemerge.py

@@ -27,10 +27,6 b' from . import ('
 from .utils import stringutil
 
 
-class CantReprocessAndShowBase(Exception):
-    pass
-
-
 def intersect(ra, rb):
     """Given two ranges return the range where they intersect or None.
 

tests/test-simplemerge.py

@@ -48,9 +48,6 b' class Merge3(simplemerge.Merge3Text):'
         )
 
 
-CantReprocessAndShowBase = simplemerge.CantReprocessAndShowBase
-
-
 def split_lines(t):
     return util.stringio(t).readlines()