package/python-secretstorage: drop Python 2 support

Since version 3.0.0, secretstorage doesn't support Python 2 anymore.
Update its reverese dependency (python-keyring) as well.

Signed-off-by: Asaf Kahlon <asafka7@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/python-keyring/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_PYTHON_KEYRING
 	bool "python-keyring"
+	depends BR2_PACKAGE_PYTHON3 # python-secretstorage
 	depends on BR2_INSTALL_LIBSTDCPP # python-secretstorage
 	select BR2_PACKAGE_PYTHON_SECRETSTORAGE # runtime
 	help

package/python-secretstorage/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_PYTHON_SECRETSTORAGE
 	bool "python-secretstorage"
+	depends on BR2_PACKAGE_PYTHON3
 	depends on BR2_INSTALL_LIBSTDCPP # python-cryptography
 	select BR2_PACKAGE_PYTHON_CRYPTOGRAPHY # runtime
 	help