Add EXFUN for `Fmap_char_attribute' in every UTF-2000.

Add EXFUN for `Fmap_char_attribute' in every UTF-2000.
(Vcharacter_composition_table): Deleted.
(Fget_composite_char): Use the implementation for external-DB support
in every UTF-2000.
(Fput_char_attribute): Likewise.
(char_attribute_system_db_file): Don't define if external-DB feature
is not available.
(Fsave_char_attribute_table): Likewise.
(Fmount_char_attribute_table): Likewise.
(Fclose_char_attribute_table): Likewise.
(Freset_char_attribute_table): Likewise.
(Fload_char_attribute_table): Likewise.
(syms_of_chartab): Don't define `save-char-attribute-table',
`mount-char-attribute-table', `reset-char-attribute-table',
`close-char-attribute-table' and `load-char-attribute-table' if
external-DB feature is not available.
(vars_of_chartab): Don't setup `Vcharacter_composition_table'.