do not clear output kernel module directory

When using an archive to provide kernel modules, the archive is directly
expanded into the output directory. The output directory is currently
removed prior to that to ensure no stale modules are present if they
were removed as part of a change in an incremental build.

Unfortunately if kernel modules are also provided via the regular
BOARD_*_KERNEL_MODULES macros, the removal of the output kernel module
directory will race with the copying of kernel modules in
BOARD_*_KERNEL_MODULES, resulting in some of those kernel modules not
being present in the output.

Kernel modules removed from BOARD_*_KERNEL_MODULES do not currently get
removed from the output directory in an incremental build anyway. So in
order to support using BOARD_*_KERNEL_MODULES and
BOARD_*_KERNEL_MODULES_ARCHIVE conurrently, take out the removal of the
output directory prior to archive expansion.

Bug: 149866863
Change-Id: Ib373650ddcb0fb5782a13d68a8869a9117e42ccc