Revert "Follow a suggestion from libtoolize:"

Sadly, older versions of autoconf - such as the ones on the OS X buildbots - don't know about AC_CONFIG_MACRO_DIRS.

This reverts commit 89291ad4f3293893387b385a0800cad42215ddd4.

Change-Id: Ie4fa71062886f58c7f6014f6b7969921f0b824ae
Reviewed-on: https://code.wireshark.org/review/5116
Reviewed-by: Guy Harris <guy@alum.mit.edu>