Fix #14: better active window detection

lua/hardline/common.lua

@@ -1,5 +1,4 @@
-local cmd, fn = vim.cmd, vim.fn
-local g = vim.g
+local cmd = vim.cmd
 local fmt = string.format
 local M = {}
 
@@ -24,10 +23,6 @@ function M.echo(hlgroup, msg)
   cmd('echohl None')
 end
 
-function M.is_active()
-  return g.statusline_winid == fn.win_getid()
-end
-
 function M.set_cache_autocmds(augroup)
   cmd(fmt('augroup %s', augroup))
   cmd('autocmd!')