Drop VERTICAL_SCROLL_BAR_WIDTH_TRIM. For X, it is zero since 1999,

Drop VERTICAL_SCROLL_BAR_WIDTH_TRIM.  For X, it is zero since 1999,
and it is always zero for others, so I assume that this is an ancient
leftover which nobody will want to change any more.
* xterm.h, w32term.h, nsterm.h (VERTICAL_SCROLL_BAR_WIDTH_TRIM): Remove.
(VERTICAL_SCROLL_BAR_INSIDE_WIDTH):
* frame.c (x_set_scroll_bar_width):
* w32fns.c (w32_createscrollbar):
* w32term.c (w32_set_vertical_scroll_bar):
* xfns.c (x_set_scroll_bar_default_width):
* xterm.c (XTflash, x_scroll_bar_create, XTset_vertical_scroll_bar)
(x_scroll_bar_expose): Related users changed.