cperl-mode.el: Make commands and options for Perl info pages obsolete.

cperl-mode.el: Make commands and options for Perl info pages obsolete.

The Perl documentation in info format is no longer distributed with Perl,
nor is it available from CPAN.   Point to cperl-perldoc instead.

* lisp/progmodes/cperl-mode.el (cperl-info-page): Make obsolete.
(cperl-tips): Remove outdated instructions to get Perl info
sources from the docstring.
(cperl-praise): Remove advertising the info interface in the
docstring.
(cperl-mode-map): Replace bindings to `cperl-info-on-command' and
`cperl-info-on-current-command' by `cperl-perldoc'.
(cperl-menu): Remove menu entries pointing to the Perl info page.
(cperl-mode): Remove explanation of the Perl info commands from
the docstring.
(cperl-info-on-command, cperl-info-on-current-command),
(cperl-imenu-info-imenu-search, cperl-imenu-on-info): Declare the
commands obsolete.

* etc/NEWS: Describe the obsoletion of Perl info commands.