revert: keep EMAIL_BACKEND as plain assignment in local settings

maildev is always available via docker-compose, no need for env var
configurability here.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: JacobCoffee

pydotorg/settings/local.py

@@ -32,10 +32,7 @@
     },
 }
 
-EMAIL_BACKEND = config(
-    'EMAIL_BACKEND',
-    default='django.core.mail.backends.smtp.EmailBackend',
-)
+EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'
 EMAIL_HOST = config('EMAIL_HOST', default='maildev')
 EMAIL_PORT = config('EMAIL_PORT', default=1025, cast=int)