ui/treemacs: remove hl-line->region face remapping
ui/treemacs: remove hl-line->region face remapping

This causes more issues that solves. Perhaps something can be done
upstream to make this line highlight brighter.

Possibly addresses #957

hlissner/doom-emacs,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,UndeadKernel/emacs_doom,UndeadKernel/emacs_doom,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/doom-emacs,UndeadKernel/emacs_doom,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/doom-emacs,hlissner/doom-emacs,UndeadKernel/emacs_doom,hlissner/.emacs.d