ui/urwid: remove urwid ui

It was too similar and inferior to curses.

README.md

@@ -12,23 +12,18 @@ Relive the great adventure… this time in the terminal realm!
 
 - Faithful port of the game logic
 - Saves (with backups) to `$XDG_CONFIG_HOME/pqcli/save.dat`
-- Terminal interface that comes in 3 flavors:
-    - Rich and colorful, but CPU intensive (`--urwid`)
-    - Simple, but easy on CPU, friendly for embedded environments (`--curses`)
+- Terminal interface that comes in 2 flavors:
+    - Rich and colorful (`--curses`, default)
     - Minimal, suitable for raw grind (`--basic`)
 - Ideal to run on your server
 
 ## How it looks like
 
-Urwid version:
-
-![Screenshot](screen-urwid.png)
-
-Curses version:
+Curses interface:
 
 ![Screenshot](screen-curses.png)
 
-Basic version:
+Basic interface:
 
 ![Screenshot](screen-basic.png)