Before:
  runtime ale_linters/systemd/systemd_analyze.vim

After:
  call ale#linter#Reset()

Execute(The systemd-analyze handler should parse lines correctly):
  AssertEqual
  \ [
  \   {
  \     'lnum': 9,
  \     'col': 1,
  \     'type': 'W',
  \     'text': 'Unknown key name ''Wat'' in section ''Service'', ignoring.',
  \   },
  \ ],
  \ ale_linters#systemd#systemd_analyze#Handle(bufnr(''), [
  \   '/home/user/.config/systemd/user/foo.service:9: Unknown key name ''Wat'' in section ''Service'', ignoring.',
  \ ])