[lldb][utils] Remove Python 2 compatibility code in lui scripts

Queue was renamed to queue in Python 3:
https://docs.python.org/3/whatsnew/3.0.html#library-changes

We require Python >= 3.8.

lldb/utils/lui/lui.py

@@ -17,11 +17,7 @@ from optparse import OptionParser
 import os
 import signal
 import sys
-
-try:
-    import queue
-except ImportError:
-    import Queue as queue
+import queue
 
 import debuggerdriver
 import cui

lldb/utils/lui/sandbox.py

@@ -14,10 +14,7 @@ import os
 import signal
 import sys
 
-try:
-    import queue
-except ImportError:
-    import Queue as queue
+import queue
 
 import cui