toolchain/gcc: remove 4.6.3, it is unused and unmaintained

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37924 3c298f89-4303-0410-b956-a3cf2f4a3e73
Merge branch 'master', remote branch 'bb/master'