Modify erc-mode-map in module definitions

Modify erc-mode-map in module definitions

* lisp/erc/erc-button.el (erc-button-mode, erc-button-enable,
erc-button-disable): Replace call to `erc-button-setup' with one to
`erc--modify-local-map'.  This means `erc-button-setup' is now dead
code from a client perspective.
* lisp/erc/erc-goodies.el (erc-irccontrols-enable,
erc-irccontrols-disable, erc-irccontrols-mode): Bind
`erc-toggle-interpret-controls' in module definition so it's only
available when the module is active.
* lisp/erc/erc-log.el (erc-log-mode, erc-log-enable, erc-log-disable):
Move top-level `define-key' into module definition.
* lisp/erc/erc-match.el (erc-match-mode, erc-match-enable,
erc-match-disable): Move top-level `define-key' into module
definition.
* lisp/erc/erc.el (erc-mode-map): Remove C-c C-c binding for
`erc-toggle-interpret-controls'.
(erc--modify-local-map): Add helper for global modules to use when
modifying `erc-mode-map'.
* test/lisp/erc/erc-tests.el (erc--modify-local-map): Add test.
Ensure modifications to `erc-mode-map' on loading `erc' and via
`erc-mode-hook' still work.  (Bug#60954.)