config: replace deprecated AC_HELP_STRING with AS_HELP_STRING
config: replace deprecated AC_HELP_STRING with AS_HELP_STRING

This silences an Automake warning.

Signed-off-by: Gaetan Nadon <8a8cc541338200f67d4d0bcb65c78b6166649462@videotron.ca>

rsaxvc/xDisapprovingEyes,rsaxvc/xDisapprovingEyes