[ng] diagnostic: don't bother explicitly rejecting ansi2knr stuff

[ng] diagnostic: don't bother explicitly rejecting ansi2knr stuff

That is, fail through the usual avenues ("possibly undefined macro
'AM_C_PROTOTYPES', "option 'ansi2knr' not recognized") rather than
giving a special error message "automatic de-ANSI-fication support
has been removed".  Since the removal has taken place in Automake 1.12
already, people will have got used to it once Automake-NG gets stable
enough.

* lib/Automake/Options.pm (_process_option_list): Remove special
handling of 'ansi2knr' option.
* m4/protos.m4: Remove.
* Makefile.am (dist_automake_ac_DATA): Adjust.
* t/ansi2knr-no-more.sh: Remove.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>