kbuild: drop bogus "common/barebox_default_env*" from CLEAN_FILES
Since commit 7fa10256c3f4 (defaultenv: Allow multiple
defaultenvironment overlays), barebox_default_env* is created
in the defaultenv/ directory. They are cleaned up when
"make clean" descends into the defaultenv/ directory.
We can simply delete "common/barebox_default_env*" from the
top Makefile.
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>