license.bbclass: don't mark it as 'nostamp'

'nostamp' is normally used for some standalone tasks like clean, checkuri, etc.
It doesn't make sense to mark do_populate_lic as 'nostamp', which is depended
by do_package. No stamp file in the build dependency chain implicates that
do_package needs to be reinvoked and thus further do_package_write* stuff.

This together with another sstate bug fully confused recent master, that people
keep observing unnecessary do_package rebuilt with or without change. Below is
a short explanation for two behaviors we observed:

a) a fresh build, and then bitbake same target w/o any change. User will observe
one unnecessary rebuild and then later rebuild is fine:
    [1st rebuild]
    * do_populate_lic has no stamp, and thus do_package is thought not current
    * do_package_setscene is then invoked with stamp file created
    * then later do_package_write*** also are rebuilt
    [2nd and later rebuild]
    * do_populate_lic has no stamp, and thus do_package is thought not current
    * do_package_setscene has stamp file and thus no need to re-execute setscene
    * thus no further rebuild required

b) a fresh build, and then adjust order of PACKAGE_CLASSES. There's one bug
regarding to PACKAGE_CLASSES and do_package_setscene, that only switch the
order in PACKAGE_CLASSES generates different checksum. In this case user may
observe up to 3 rebuilds when switching package_rpm/package_ipk back and forth.

Signed-off-by: Lianhao Lu <lianhao.lu@intel.com>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>

meta/classes/license.bbclass

@@ -11,7 +11,6 @@
 LICENSE_DIRECTORY ??= "${DEPLOY_DIR_IMAGE}/licenses"
 
 addtask populate_lic after do_patch before do_package 
-do_populate_lic[nostamp] = "1"
 python do_populate_lic() {
     """
     Populate LICENSE_DIRECTORY with licenses.