Remove Motif FAQ as outdated

Nobody uses wxMotif for anything, and nobody should consider using it for
anything. Even if somebody does use wxMotif for something (unlikely, as it
is in totally unusable), this FAQ barely has any useful information.

See #112.

Author: lanurmi

docs/faq/index.md

@@ -9,7 +9,6 @@ Welcome to the wxWidgets FAQ. Please select a category:
 * [Windows Specific Questions](/docs/faq/windows/)
 * [macOS Specific Questions](/docs/faq/osx/)
 * [GTK+ Specific Questions](/docs/faq/gtk/)
-* [Motif Specific Questions](/docs/faq/motif/)
 * [X11 Specific Questions](/docs/faq/x11/)
 
 For further information, please see the build and install instructions for the individual