Clean up pointer blanking code

Clean up pointer blanking code

* src/xterm.c (XTtoggle_invisible_pointer): Dispatch to correct
function directly.
(x_probe_xfixes_extension): Return directly based on dpyinfo.
(xfixes_toggle_visible_pointer): Make conditional on
`HAVE_XFIXES'.
(make_invisible_cursor): Initialize `c' correctly.
(x_toggle_visible_pointer): Handle cursor allocation failures.
(x_free_frame_resources): Dispatch with
XTtoggle_visible_pointer.
(x_setup_pointer_blanking): Delete function.
(x_term_init): Initialize blank cursor here instead.
* src/xterm.h (struct x_display_info): New field
`fixes_pointer_blanking'.