Don't update width of prompt area

Fixes gh-9331 (roughly)

The input prompts are now displayed through prompt_toolkit, so this code
doesn't know the width it's trying to match.

IPython/core/prompts.py

@@ -403,10 +403,10 b' class PromptManager(Configurable):'
 
         # Handle justification of prompt
         invis_chars = self.invisible_chars[name] if color else 0
-        self.txtwidth = _lenlastline(res) - invis_chars
+        # self.txtwidth = _lenlastline(res) - invis_chars
         just = self.justify if (just is None) else just
         # If the prompt spans more than one line, don't try to justify it:
         if just and name != 'in' and ('\n' not in res) and ('\r' not in res):
             res = res.rjust(self.width + invis_chars)
-        self.width = _lenlastline(res) - invis_chars
+        # self.width = _lenlastline(res) - invis_chars
         return res