Remove unused variable assignments (aws#138)

Author: seanmcl

src/aws_encryption_sdk/key_providers/kms.py

@@ -43,8 +43,6 @@ def _region_from_key_id(key_id, default_region=None):
     """
     try:
         region_name = key_id.split(":", 4)[3]
-        if default_region is None:
-            default_region = region_name
     except IndexError:
         if default_region is None:
             raise UnknownRegionError(

src/aws_encryption_sdk/materials_managers/caching.py

@@ -214,7 +214,7 @@ def get_encryption_materials(self, request):
             return new_result
 
         # Add results into cache
-        cache_entry = self.cache.put_encryption_materials(
+        self.cache.put_encryption_materials(
             cache_key=cache_key,
             encryption_materials=new_result,
             plaintext_length=request.plaintext_length,