Revert "Fix #14: better active window detection"

This reverts commit 680cfeb074.

lua/hardline/common.lua

@@ -1,4 +1,5 @@
-local cmd = vim.cmd
+local cmd, fn = vim.cmd, vim.fn
+local g = vim.g
 local fmt = string.format
 local M = {}
 
@@ -23,6 +24,10 @@ 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!')