Deprecate option erc-remove-parsed-property

Deprecate option erc-remove-parsed-property

* etc/ERC-NEWS: Add entry for `erc-remove-parsed-property'.
* lisp/erc/erc.el (erc-remove-parsed-property): Deprecate option
because the potential for inadvertent self harm outweighs the
potential benefits.  Additionally, replicating this functionality via
hooks is trivial.
(erc-display-line-1): Remove quasi-deprecated `tags' property because
the preferred format for `erc-response.tags' has changed, and ERC has
never supported IRCv3 tags.