(char-db-ignored-attributes): Add `composition'.

(char-db-ignored-attributes): Add `composition'.
(char-db-json-insert-relation-feature): Use
`char-db-json-insert-char-spec' even if running with readable mode.
(char-db-json-insert-char-features):
- Delete line-breaking for `=>ucs' and `=>ucs*'.
- Delete setting for `japanese-radical', `ideographic-',
  `->ideograph', `ideograph=', `original-ideograph-of',
  `ancient-ideograph-of', `vulgar-ideograph-of', `wrong-ideograph-of'
  and `ideographic-variants' because they have been already abolished.
(what-char-definition-json): Use `char-db-json-char-data-with-variant'
with readable mode.