package/simicsfs: remove package

Buildroot currently packages version 1.18 of simics, which is quite
out of date, and does not compile with Linux 4.12+. The latest package
v1.22 supports recent kernels, however that is not publicly available
anymore like the older versions.

In fact Simics is now moving away from the simicsfs kernel module, as
the kernel module has required too much maintenance work. Users should
move to the new user mode Simics agent instead. Therefore, we drop the
corresponding package from Buildroot.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>