Remove a few more code parts which are unused on Linux

Remove a few more code parts which are unused on Linux

This change is abapted from Dmitry's changes to remove support for
non-Linux architectures.

* Makefile.am: Remove if LINUX/endif pairs.
* defs.h: Remove stream_ioctl() declaration.
* ioctl.c (ioctl_decode): Remove 'ifdef HAVE_SYS_STREAM_H' block.
* resource.c: Use 'defined(FOO)' instead of 'defined FOO' form.
* util.c: Likewise.
* signal.c: Remove conditional includes which are never used on Linux.
* stream.c: Likewise.
* file.c: Remove excessive empty lines.

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>