doc: remove obsolete PERL_PATH
doc: remove obsolete PERL_PATH

This fixes the following warning:

warning: Tag 'PERL_PATH' at line 110 of file 'Doxyfile' has become obsolete.

Signed-off-by: Alexander Stein <dbef83f64948dc68aad31596bbf6991154a9d730@mailbox.org>
Signed-off-by: Bartosz Golaszewski <e5d45fddd9040473413b909b802f629a971ad04c@baylibre.com>

brgl/libgpiod,brgl/libgpiod,brgl/libgpiod,brgl/libgpiod