Revert "Add custom LTI exception."

This reverts commit ef4b7b9b.

common/lib/xmodule/xmodule/exceptions.py

@@ -31,11 +31,3 @@ class SerializationError(Exception):
     def __init__(self, location, msg):
         super(SerializationError, self).__init__(msg)
         self.location = location
-
-
-class LTIError(Exception):
-    """
-    An error occured when parsing LTI paramaters from
-    course settings or LTI unit
-    """
-    pass

common/lib/xmodule/xmodule/lti_module.py

@@ -14,7 +14,6 @@ import urllib
 
 from xmodule.editing_module import MetadataOnlyEditingDescriptor
 from xmodule.x_module import XModule
-from xmodule.exceptions import LTIError
 from xmodule.course_module import CourseDescriptor
 from pkg_resources import resource_string
 from xblock.core import String, Scope, List