Simplify highlighting: remove SneakCursor

`SneakCursor` was added as a workaround for the case where the user's
`Cursor` highlight was broken. But with 'termguicolors', there are more
cases to consider (also: `has('gui_running')` is meaningless in Nvim).

Instead of adding more handling, just use `Cursor`. If the user has
a broken Cursor highlight, it's better that they fix it.

autoload/sneak/hl.vim

@@ -50,12 +50,6 @@ func! s:init() abort
   if 0 == hlID("SneakLabelMask")  " fg same as bg
     exec 'highlight SneakLabelMask guifg='.guibg.' guibg='.guibg.' ctermfg='.ctermbg.' ctermbg='.ctermbg
   endif
-
-  if has('gui_running') || -1 != match(sneak#hl#get('Cursor'), 'ctermbg')
-    highlight link SneakCursor Cursor
-  else
-    highlight link SneakCursor SneakScope
-  endif
 endf
 
 augroup sneak_colorscheme " re-init if :colorscheme is changed at runtime. #108

autoload/sneak/label.vim

@@ -137,7 +137,7 @@ func! s:before()
   ownsyntax sneak_label
 
   " highlight the cursor location (else the cursor is not visible during getchar())
-  let w:sneak_cursor_hl = matchadd("SneakCursor", '\%#', 11, -1)
+  let w:sneak_cursor_hl = matchadd("Cursor", '\%#', 11, -1)
 
   let s:cc_orig=&l:concealcursor | setlocal concealcursor=ncv
   let s:cl_orig=&l:conceallevel  | setlocal conceallevel=2