Remove and update documentation

This change is a verbatim part of Dmitry's changes to remove support
for non-Linux architectures.

* PORTING: Deleted.
* INSTALL: Modified.
* README: Modified.
* strace.1: Modified: bugs should be reported to mailing list, not Debian.
* strace.spec: do not install PORTING file.

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/strace.1 b/strace.1
index 222a0cb..4c007cd 100644
--- a/strace.1
+++ b/strace.1
@@ -743,7 +743,6 @@
 .SH PROBLEMS
 Problems with
 .B strace
-should be reported via the Debian Bug Tracking System,
-or to the
+should be reported to the
 .B strace
 mailing list at <strace\-devel@lists.sourceforge.net>.