devtool.py: change to do clean before remove-layer
if do clean after remove-layer, it will make stamp file not cleaned
since variable STAMP has changed, this will cause error like:
if testcase buildclean failed, when run next testcase modify, since
do_prepare_recipe_sysroot's stamp file exists, sysroot not populated,
then do_compile will fail with error:
/bin/sh: x86_64-poky-linux-gcc: command not found
Signed-off-by: Changqing Li <changqing.li@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
