python-mimeparse: remove SOURCE variable

The SOURCE variable has the default value, so it is not necessary, as
reported by check-package:

package/python-mimeparse/python-mimeparse.mk:8: remove default value of _SOURCE variable

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/python-mimeparse/python-mimeparse.mk

@@ -5,7 +5,6 @@
 ################################################################################
 
 PYTHON_MIMEPARSE_VERSION = 1.6.0
-PYTHON_MIMEPARSE_SOURCE = python-mimeparse-$(PYTHON_MIMEPARSE_VERSION).tar.gz
 PYTHON_MIMEPARSE_SITE = https://files.pythonhosted.org/packages/0f/40/ac5f9e44a55b678c3cd881b4c3376e5b002677dbeab6fb3a50bac5d50d29
 PYTHON_MIMEPARSE_SETUP_TYPE = setuptools
 PYTHON_MIMEPARSE_LICENSE = MIT