xen/bitmap: Drop {bitmap,cpumask,nodes}_shift_{left,right}()

xen/bitmap: Drop {bitmap,cpumask,nodes}_shift_{left,right}()

These operations have never been used in Xen since their introduction, and it
doesn't seem likely that they will in the future.

Bloat-o-meter reports that they aren't the smallest when compiled, either.

  add/remove: 0/2 grow/shrink: 0/0 up/down: 0/-814 (-814)
  Function                                     old     new   delta
  __bitmap_shift_left                          366       -    -366
  __bitmap_shift_right                         448       -    -448
  Total: Before=3323730, After=3322916, chg -0.02%

Suggested-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>