Remove throwaway Rust HttpClient constructions from tests

These existed only to force the tokio thread pool to start before
reactor.run() under the old callWhenRunning-based startup. Now that the
pool starts lazily on first use, the constructions (and the
make_homeserver overrides that existed solely to host them) are dead
weight. The tearDown hooks that fire the reactor shutdown triggers stay:
they are still what stops the tokio pool for tests that exercise the
Rust /versions handler.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HyuiV3m44ZbK9o24EnMMES

tests/rest/client/test_matrixrtc.py

@@ -22,7 +22,6 @@ from twisted.internet.testing import MemoryReactor
 from synapse.rest import admin
 from synapse.rest.client import login, matrixrtc, register, room, versions
 from synapse.server import HomeServer
-from synapse.synapse_rust.http_client import HttpClient
 from synapse.util.clock import Clock
 
 from tests import unittest
@@ -112,19 +111,6 @@ class MatrixRtcVersionsTestCase(HomeserverTestCase):
 
     servlets = [versions.register_servlets]
 
-    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
-        hs = self.setup_test_homeserver()
-
-        self._http_client = hs.get_proxied_http_client()
-        # The tokio thread pool is started lazily on first use, so no
-        # reactor startup hooks need to run here.
-        _ = HttpClient(
-            runtime=hs.get_rust_runtime(),
-            user_agent=self._http_client.user_agent.decode("utf8"),
-        )
-
-        return hs
-
     def tearDown(self) -> None:
         # MemoryReactor doesn't trigger the shutdown phases, and we want the
         # Tokio thread pool to be stopped