build-sys: remove DEFAULT_INCLUDES workaround

build-sys: remove DEFAULT_INCLUDES workaround

The automake stuff uses "-I.". as a default gcc option for includes. This is a
problem for source code where is local includes with a same name like system
includes (e.g.  mntent.h, paths.h). Possible workaround is overwrite the
automake DEFAULT_INCLUDES variable. But this solution produces warnings. The
best way (this patch) is probably rename the files and remove DEFAULT_INCLUDES.

Signed-off-by: Karel Zak <kzak@redhat.com>