bug#29053: 26.0.90: scroller cannot be dragged to bottom of window

[Charles A. Roelli]

Seems that reverting this commit removes the issue:

  commit e683a2570be6f2e4f8defa4e7ee35a7d87f18918
  Author: Alan Third <alan@idiocy.org>
  Ref:    tags/emacs-26.0.90~2038
  Date:   Sun May 1 13:04:07 2016 +0200

  Implement horizontal scroll bars on NS

  * lisp/scroll-bar.el (horizontal-scroll-bars-available-p): Remove NS
  check.
  * lisp/term/ns-win.el: Remove custom NS scroll-bar handlers and bind
  scroll-bar mouse clicks to standard handlers.
  * src/nsterm.h (EmacsScroller): Add 'horizontal' property and rename
  pixel_height to pixel_length.
  * src/nsterm.m (x_set_window_size): Remove left-hand scroll-bar code. It
  caused scroll-bars to be over-drawn and the best working solution
  appears to be complete removal.
  (ns_set_horizontal_scroll_bar): Rewrite to handle horizontal scrollers
  correctly.
  (ns_set_vertical_scroll_bar): Set width to actual scroller width.
  (setFrame): Handle horizontal case.
  (dealloc): Handle horizontal case.
  (judge): Handle horizontal case.
  (setPosition): Rename pixel_height to pixel_length.
  (sendScrollEventAtLoc): Handle horizontal case.
  (mouseDown): Handle horizontal case and general tidy up of code.
  (mouseDragged): Handle horizontal case. Call sendScrollEventAtLoc with
  absolute pixel size instead of ratio.
  * src/window.h: Remove NS check.

macOS 10.6 is probably a special case.