remove read_password_func from cli handler

remove read_password_func from cli handler

we have a param_mapping now, with which we can impement that

e.g. instead of using:

sub read_password {
    # read password
}

we can do:

sub param_mapping {
    my ($name) = @_;

    my $password_map = ['password', sub{
	# read password
    }, '<password', 1];

    my $mapping = {
	'apicall1' => [$password_map],
	'apicall2' => [$password_map],
	...
    };

    return $mapping->{$name};
}

this has the advantage that we can use different subs for different
api calls (e.g. pveum passwd vs pveum ticket)

if a CLIHandler implemenation still has a read_password sub and no
param_mapping, we generate one for them with read_password as the
sub for the standard mapping 'pve-password'

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>