💥(sentry) remove DJANGO_ before Sentry DSN env variable

Other "La Suite" projects don't have the "DJANGO_" prefix, so
we align this project with others.

src/backend/people/settings.py

@@ -74,7 +74,7 @@ class Base(Configuration):
     You may also want to override default configuration by setting the following environment
     variables:
 
-    * DJANGO_SENTRY_DSN
+    * SENTRY_DSN
     * DB_NAME
     * DB_HOST
     * DB_PASSWORD
@@ -341,7 +341,7 @@ class Base(Configuration):
     CORS_ALLOWED_ORIGIN_REGEXES = values.ListValue([])
 
     # Sentry
-    SENTRY_DSN = values.Value(None, environ_name="SENTRY_DSN")
+    SENTRY_DSN = values.Value(None, environ_name="SENTRY_DSN", environ_prefix=None)
 
     # Easy thumbnails
     THUMBNAIL_EXTENSION = "webp"
@@ -1066,10 +1066,6 @@ class Production(Base):
             },
         },
     }
-    SENTRY_DSN = values.Value(
-        None,
-        environ_name="SENTRY_DSN",
-    )
 
 
 class Feature(Production):