.wikiheaders-options: Don't warn about missing symbols.

This just spams Ryan's email, for a legacy branch we aren't going to spend
time documenting further.

Author: icculus

.wikiheaders-options

@@ -12,5 +12,5 @@ selectheaderregex = \ASDL_image\.h\Z
 projecturl = https://libsdl.org/projects/SDL_image
 wikiurl = https://wiki.libsdl.org/SDL_image
 bugreporturl = https://github.com/libsdl-org/sdlwiki/issues/new
-warn_about_missing = 1
+warn_about_missing = 0
 wikipreamble = (This function is part of SDL_image, a separate library from SDL.)