classes/license.bbclass: Don't copy unneeded licenses by package
Usually a recipe only provides one package but when provides more
than one package the LICENSE variable per package (i.e. linux-firmware)
needs to take into account to avoid unnecesary copy of licenses into
packages.
The patch validates if LICENSE exists in package LICENSES in order to
don't copy unneeded licenses.
As result of this patch some packages will not contain licenses there
are not into LICENSE variable.
For example:
acl contains GPLv2+ instead of GPLv2+ and LGPLv2.1+
libacl contains LGPLv2+ instead of GPLv2+ and LGPLv2.1+
This behaviour is declared on the acl recipe as:
SUMMARY = "Utilities for managing POSIX Access Control Lists"
HOMEPAGE = "http://savannah.nongnu.org/projects/acl/"
SECTION = "libs"
