Do not create man page links with doxygen

There is a lot of files created with .so links to non-installed
files, making most of installed pages useless. The files
referenced in .so links are not suitable for installation nor
do they contain any useful information for them to be worth
fixing.

Signed-off-by: Armin Krezović <krezovic.armin@gmail.com>
Acked-by: Daniel Stone <daniels@collabora.com>