oeqa/selftest/lic_checksum: Cleanup changes to emptytest include

oeqa/selftest/lic_checksum: Cleanup changes to emptytest include

Config written to the emptytest include file is invalid after the test
has cleaned up its temporary directories resulting in the emptytest
recipe potentially having invalid content when parsed by successive
bitbake runs.

This presents the following error in tests after lic_checksum execution,
e.g. 'oe-selftest -r lic_checksum recipetool'

  ERROR: .../emptytest.bb: Unable to get checksum for emptytest SRC_URI entry tmpn_nyosnq: file could not be found

Remove the recipe include content once the bitbake runs are completed in
each lic_checksum test case.

Signed-off-by: Nathan Rossi <nathan.rossi@digi.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>