s390: make 'install' not depend on vmlinux

s390: make 'install' not depend on vmlinux

[ Upstream commit 94e90f727f7424d827256023cace829cad6896f4 ]

For the same reason as commit 19514fc665ff ("arm, kbuild: make "make
install" not depend on vmlinux"), the install targets should never
trigger the rebuild of the kernel.

The variable, CONFIGURE, is not set by anyone. Remove it as well.

Link: https://lkml.kernel.org/r/20200216144829.27023-1-masahiroy@kernel.org
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>