refactor: move xml_importer-specific exceptions into xml_importer

This is a minor refactoring in order to remove
a code dependency of ./xmodule on ./cms

cms/djangoapps/contentstore/exceptions.py

@@ -1,45 +1,15 @@
 """
 A common module for managing exceptions. Helps to avoid circular references
 """
-from .errors import ERROR_WHILE_READING, FAILED_TO_IMPORT_MODULE
-
-
-class CourseImportException(Exception):
-    """Base exception class for course import workflows."""
-
-    def __init__(self):
-        super().__init__(self.description)  # pylint: disable=no-member
-
-
-class ErrorReadingFileException(CourseImportException):
-    """
-    Raised when error occurs while trying to read a file.
-    """
-
-    def __init__(self, filename, **kwargs):
-        self.description = ERROR_WHILE_READING.format(filename)
-        super().__init__(**kwargs)
-
-
-class ModuleFailedToImport(CourseImportException):
-    """
-    Raised when a module is failed to import.
-    """
-
-    def __init__(self, display_name, location, **kwargs):
-        self.description = FAILED_TO_IMPORT_MODULE.format(display_name, location)
-        super().__init__(**kwargs)
 
 
 class AssetNotFoundException(Exception):
     """
     Raised when asset not found
     """
-    pass  # lint-amnesty, pylint: disable=unnecessary-pass
 
 
 class AssetSizeTooLargeException(Exception):
     """
     Raised when the size of an uploaded asset exceeds the maximum size limit.
     """
-    pass  # lint-amnesty, pylint: disable=unnecessary-pass