Revert "Add Isotammi addons to Project Manager defaults"

This reverts commit 52849a6.

Author: Nick-Hall

gramps/gen/config.py

@@ -186,12 +186,7 @@ def emit(key):
             "Gramps",
             "https://raw.githubusercontent.com/gramps-project/addons/master/gramps52",
             True,
-        ],
-        [
-            "Isotammi",
-            "https://raw.githubusercontent.com/Taapeli/isotammi-addons/master/addons/gramps52",
-            False,
-        ],
+        ]
     ],
 )
 register("behavior.addons-allow-install", False)