ui: Remove/adapt some old code for a big UI refactor

- Remove abstract_ui global, now it is always active
- Remove some terminal handling code
- Remove unused functions
- Remove HAVE_TGETENT/TERMINFO/TERMIOS/IOCTL #ifdefs
- Remove tgetent/terminfo from version.c
- Remove curses/terminfo dependencies
- Only start/stop termcap when starting/exiting the program
- msg_use_printf will return true if there are no attached UIs(
  messages will be written to stdout)
- Remove `ex_winpos`(implement `:winpos` with `ex_ni`)

src/nvim/version.c

@@ -136,21 +136,6 @@ static char *(features[]) = {
   "+tag_binary",
   "+tag_old_static",
   "-tag_any_white",
-#if defined(UNIX)
-
-  // only Unix can have terminfo instead of termcap
-# ifdef TERMINFO
-  "+terminfo",
-# else // ifdef TERMINFO
-  "-terminfo",
-# endif // ifdef TERMINFO
-#else   // unix always includes termcap support
-# ifdef HAVE_TGETENT
-  "+tgetent",
-# else  // ifdef HAVE_TGETENT
-  "-tgetent",
-# endif  // ifdef HAVE_TGETENT
-#endif  // if defined(UNIX)
   "+termresponse",
   "+textobjects",
   "+title",
@@ -813,19 +798,6 @@ static char *(extra_patches[]) = {
   NULL
 };
 
-int highest_patch(void)
-{
-  int i;
-  int h = 0;
-
-  for (i = 0; included_patches[i] != 0; ++i) {
-    if (included_patches[i] > h) {
-      h = included_patches[i];
-    }
-  }
-  return h;
-}
-
 /// Checks whether patch `n` has been included.
 ///
 /// @param n The patch number.