Use input instead of raw_input in gdbclient.py

Following suggestions in b/194659728, update the python script to work
under python3.

Previous failure:

Traceback (most recent call last):
  File "/android3/android/master/development/scripts/lldbclient.py", line 413, in <module>
    main()
  File "/android3/android/master/development/scripts/lldbclient.py", line 405, in main
    do_main()
  File "/android3/android/master/development/scripts/lldbclient.py", line 400, in do_main
    raw_input("Press enter to shut down lldb-server")
NameError: name 'raw_input' is not defined

Bug: none
Test: "lldbclient.py --setup-forwarding vscode-lldb -r
/data/nativetest64/inputflinger_tests/inputflinger_tests
--gtest_filter=PalmRejectorTest.GenericAxisValue_IsNotSet"

Change-Id: I21d977cbc580894d6e2eb2f2f56dec04c65b0416
diff --git a/scripts/gdbclient.py b/scripts/gdbclient.py
index bb92151..b9764cd 100755
--- a/scripts/gdbclient.py
+++ b/scripts/gdbclient.py
@@ -397,7 +397,7 @@
                         lldb-server connection. Press enter in this terminal once debugging is
                         finished to shut lldb-server down and close all the ports."""))
             print("")
-            raw_input("Press enter to shut down lldb-server")
+            input("Press enter to shut down lldb-server")
 
 
 def main():