Remove all Neovim statuslines and add a window separator at the bottom of the screen.

global-winsep.vim

" Quick 'n dirty Vim script for Neovim that removes all statuslines and creates
" a global statusline acting as a fake window separator.
" Also sets 'cmdheight' to 0.

hi! link StatusLine WinSeparator
hi! link StatusLineNC WinSeparator

func! Stl() abort
    let hc = &ambw == 'single' ? '─' : '-'
    let uc = &ambw == 'single' ? '┴' : '-'
    let str = ''
    for w in range(1, winnr('$'))
        if win_gettype(w) ==# 'popup' | break | endif
        let info = getwininfo(win_getid(w))[0]
        if info.winrow + info.height + info.winbar < &lines - &ch
            continue
        endif
        let str ..= hc->repeat(info.width) .. uc
    endfor
    return str[:-len(uc) - 1]
endfunc

set ch=0 ls=3 stl=%!Stl()