[toolchain] gcc: remove support for 4.6.2

There are no good reasons for keeping this version around when 4.6.3 and
4.6-linaro are there.

Signed-off-by: Luka Perkov <luka@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35805 3c298f89-4303-0410-b956-a3cf2f4a3e73