Do not include SPDX expression in low level matches

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

src/licensedcode/match.py

@@ -792,7 +792,6 @@ def to_dict(
 
         # LicenseDB Level Information (Rule that was matched)
         result['license_expression'] = self.rule.license_expression
-        result['license_expression_spdx'] = self.rule.spdx_license_expression() 
         result['rule_identifier'] = self.rule.identifier
 
         # TODO: should be a Rule.url()  method instead