ref(seer): Remove unused supergroups.active-rca-source option

This option is used on the Seer side, not in Sentry. Remove it until
it's actually needed here.

Author: yuvmen

src/sentry/options/defaults.py

@@ -1344,11 +1344,6 @@
 )
 
 # Supergroups / Lightweight RCA
-register(
-    "supergroups.active-rca-source",
-    default="explorer",
-    flags=FLAG_AUTOMATOR_MODIFIABLE,
-)
 register(
     "supergroups.lightweight-enabled-orgs",
     type=Sequence,