Fix for emrun --kill-exit (emscripten-core#25703)

This was broken by emscripten-core#25359. I though I was just moving this assignment to
the correct place, but it seems like it broken emrun because the 1.1
protocol was not actually enabled before. Once enabled it seems like
this was causing `httpd.server_close` to hang forever.

Fixes: emscripten-core#25654

Author: sbc100

emrun.py

@@ -578,8 +578,6 @@ def shutdown(self):
 
 # Processes HTTP request back to the browser.
 class HTTPHandler(SimpleHTTPRequestHandler):
-  protocol_version = 'HTTP/1.1'  # noqa: DC01
-
   def send_head(self):
     global page_last_served_time
     path = self.translate_path(self.path)