kernel: Remove fetch target
kernel: Remove fetch target

This target allowed to locally download the kernel source
tar balls. We haven't used this foir a while and adding
v5.x kernel support for it would add yet another conditional.

Remove it to keep the Makefile simpler.

Signed-off-by: Rolf Neugebauer <bc755ac45a0e799d1d490cba76febc56d80cc5fc@rneugeba.io>

konstruktoid/linuxkit,deitch/linuxkit,furious-luke/linuxkit,furious-luke/linuxkit,konstruktoid/linuxkit,justincormack/linuxkit,JohnnyLeone/linuxkit,furious-luke/linuxkit,yankcrime/linuxkit,deitch/linuxkit,JohnnyLeone/linuxkit,djs55/linuxkit,rn/linuxkit,konstruktoid/linuxkit,rn/linuxkit,djs55/linuxkit,justincormack/linuxkit,konstruktoid/linuxkit,justincormack/linuxkit,JohnnyLeone/linuxkit,rn/linuxkit,djs55/linuxkit,linuxkit/linuxkit,JohnnyLeone/linuxkit,yankcrime/linuxkit,linuxkit/linuxkit,linuxkit/linuxkit,furious-luke/linuxkit,rn/linuxkit,deitch/linuxkit,rn/linuxkit,yankcrime/linuxkit,yankcrime/linuxkit,deitch/linuxkit,deitch/linuxkit,furious-luke/linuxkit,linuxkit/linuxkit,justincormack/linuxkit,justincormack/linuxkit,konstruktoid/linuxkit,yankcrime/linuxkit,JohnnyLeone/linuxkit,yankcrime/linuxkit,djs55/linuxkit,konstruktoid/linuxkit,linuxkit/linuxkit,justincormack/linuxkit,djs55/linuxkit