Revert "mavsdk_tests: retry gz model spawn command"

This reverts commit c15d3f7cfa.

test/mavsdk_tests/process_helper.py

@@ -8,7 +8,6 @@ import subprocess
 import shutil
 import threading
 import errno
-import select
 from typing import Any, Dict, List, TextIO, Optional
 
 
@@ -68,13 +67,7 @@ class Runner:
 
     def process_output(self) -> None:
         assert self.process.stdout is not None
-
-        poll_obj = select.poll()
-        poll_obj.register(self.process.stdout, select.POLLIN)
-
-        while not self.stop_thread.is_set():
-            poll_result = poll_obj.poll(0)
-            if poll_result:
+        while True:
             line = self.process.stdout.readline()
             if not line and \
                     (self.stop_thread.is_set() or self.poll is not None):