TUI: Do not disable BCE for builtin terminfos

Remove this vestigial hack from neovim#7624.

Since 5a0d028 we blacklist BCE more surgically. And
patch_terminfo_bugs() is the more appropriate place for that.

ref 5749eca
ref neovim#4210 neovim#4421 neovim#7035 neovim#7337 neovim#7381 neovim#7425 neovim#7618

src/nvim/tui/terminfo.c

@@ -137,9 +137,6 @@ unibi_term *terminfo_from_builtin(const char *term, char **termname)
   if (*termname == NULL) {
     *termname = xstrdup("builtin_?");
   }
-  // Disable BCE by default (for built-in terminfos). #7624
-  // https://github.com/kovidgoyal/kitty/issues/160#issuecomment-346470545
-  unibi_set_bool(ut, unibi_back_color_erase, false);
   return ut;
 }