Remove system-build section from x86, arm and mips

It was empty, only wrt has anything useful inside.
packages: Update zlib to 1.2.8
packages: Update hostapd to 2.0
packages: Update dropbear to 2013.58
packages: Update iptables to 1.4.19.1
packages: Update libnl to 3.2.22
Remove libnl patch

No longer using old git repo tarball so patch shouldn't be needed.
Remove iptables fixes patch

Updated to newer version of iptables.
Remove busybox 1.17.3 fixes patch

Moved to newer busybox version.
Remove ARM gcc soft-float patch
packages: Update e2fsprogs to 1.42.7
changelog: Updates since 2012
general: Update date