- Add autoload setting for `mu-cite-get-prefix-method',

- Add autoload setting for `mu-cite-get-prefix-method',
  `mu-cite-get-prefix-register-method' and
  `mu-cite-get-prefix-register-verbose-method'.

(mu-cite-registration-file): Deleted.
(mu-cite-obsolete-variable-alist): Deleted.
(mu-cite-obsolete-function-alist): Deleted.
(mu-cite-registration-file): Deleted [moved to mu-register.el].
(mu-cite-allow-null-string-registration): Likewise.
(mu-cite-registration-file-coding-system-for-read): Likewise.
(mu-cite-registration-file-coding-system-for-write): Deleted.
(mu-cite-registration-file-modes): Deleted [moved to mu-register.el].
(mu-cite-registration-symbol): Likewise.
(mu-cite-citation-name-alist): Likewise.
(mu-cite-minibuffer-history): Likewise.
(mu-cite-get-citation-name): Likewise.
(mu-cite-add-citation-name): Likewise.
(mu-cite-load-registration-file): Likewise.
(mu-cite-save-registration-file): Likewise.
(mu-cite-get-prefix-method): Likewise.
(mu-cite-get-prefix-register-method): Likewise.
(mu-cite-get-prefix-register-verbose-method): Likewise.
(mu-cite/allow-null-string-registration): Deleted [moved to
mu-register.el].
(mu-cite/citation-name-alist): Likewise.
(mu-cite/minibuffer-history): Deleted because there are no need.
(mu-cite/registration-file): Deleted [moved to
mu-register.el].

- Delete obsolete aliases except `mu-cite/cite-original',
  `mu-cite/get-field-value' and `mu-cite/get-value' because there are
  no need.