Ignore obsolete option --disable-keypad.

* scd/scdaemon.c (opts): Ignore --disable-keypad.

The renaming of --disable-keypad to --disable-pinpad might mess up
configuration files managed with a GUI. The GUI does not not anymore
know about the old option and would allow the user to switch
"disable-pinpad" on. However, a "disable-keypad" might still linger
in the conf file with gpgconf not knowing about it. Thus the conf
file would always be rejected and manual intervention would be
required. Ignoring the old option nicely solves the problem.