bpo-35610: IDLE - Replace .context_use_ps1 with .prompt_last_line (GH-11307)

Changes in bpo- 31858 made the less informative 'context_use_ps1' redundant.
diff --git a/Lib/idlelib/hyperparser.py b/Lib/idlelib/hyperparser.py
index 7e7e0ae..77baca7 100644
--- a/Lib/idlelib/hyperparser.py
+++ b/Lib/idlelib/hyperparser.py
@@ -35,7 +35,7 @@
             return int(float(index))
         lno = index2line(text.index(index))
 
-        if not editwin.context_use_ps1:
+        if not editwin.prompt_last_line:
             for context in editwin.num_context_lines:
                 startat = max(lno - context, 1)
                 startatindex = repr(startat) + ".0"