Clean up database branching test cases

We don't need to query or set __internal_testmode in order to create a
database from a template anymore. Clean up that code.

This will also fix a flake, probably, but we *are* planning to fix it
more properly (see #6349).

edb/testbase/server.py

@@ -1073,20 +1073,6 @@ async def setup_and_connect(cls):
         elif cls.uses_database_copies():
             admin_conn = await cls.connect()
 
-            orig_testmode = await admin_conn.query(
-                'SELECT cfg::Config.__internal_testmode',
-            )
-            if not orig_testmode:
-                orig_testmode = False
-            else:
-                orig_testmode = orig_testmode[0]
-
-            # Enable testmode to unblock the template database syntax below.
-            if not orig_testmode:
-                await admin_conn.execute(
-                    'CONFIGURE SESSION SET __internal_testmode := true;',
-                )
-
             base_db_name, _, _ = dbname.rpartition('_')
 
             if cls.get_setup_script():
@@ -1108,11 +1094,6 @@ async def setup_and_connect(cls):
                 async with tr:
                     await admin_conn.execute(create_command)
 
-            if not orig_testmode:
-                await admin_conn.execute(
-                    'CONFIGURE SESSION SET __internal_testmode := false;',
-                )
-
             await admin_conn.aclose()
 
         cls.con = await cls.connect(database=dbname)