local.conf.sample: Update BBMASK example
local.conf.sample: Update BBMASK example

Since bitbake.conf has a real BBMASK (and has for some time) we shouldn't
suggest that people start out by wiping that out.

Signed-off-by: Tom Rini <4c3d5c8f8c21c27dd329bd585f481113514551fd@mentor.com>

rascalmicro/openembedded-rascal,rascalmicro/openembedded-rascal,rascalmicro/openembedded-rascal,rascalmicro/openembedded-rascal,rascalmicro/openembedded-rascal,rascalmicro/openembedded-rascal,rascalmicro/openembedded-rascal,rascalmicro/openembedded-rascal