Remove fringe size customization

Flycheck and diff-hl make heavy use of the fringe and look better with
8-pixel wide fringe.

core/prelude-ui.el

@@ -57,11 +57,6 @@
 (column-number-mode t)
 (size-indication-mode t)
 
-;; make the fringe (gutter) smaller
-;; the argument is a width in pixels (the default is 8)
-(if (fboundp 'fringe-mode)
-    (fringe-mode 4))
-
 ;; enable y/n answers
 (fset 'yes-or-no-p 'y-or-n-p)