cmake: Really add FCGI_INCLUDE_DIR to include_directories for rgw

cmake: Really add FCGI_INCLUDE_DIR to include_directories for rgw

Commit 3cf6c53 was incorrect.  FCGI_INCLUDE_DIR doesn't need to be
set in src/rgw/CMakeLists.txt, but it does need to be set for the
rgw_a target in src/CMakeLists.txt, as well as for the
ceph_test_librgw_file and ceph_test_librgw_file_nfsns targets in
src/test/CMakeLists.txt.  I can only assume that I must not have
done a completely clean rebuild at some point when testing a
reworked version of the earlier commit :-/

This is only a problem for distros that keep the FCGI headers in
/usr/include/fastcgi/ (e.g.: SUSE).

This commit also removes a redundant include of <fcgiapp.h>

Signed-off-by: Tim Serong <tserong@suse.com>