#4454 Clean up root test directory tests

Combine cases into smaller tests of tests and remove tests we no longer
need. Linter tests have been moved to where they should be.

test/test_deferred_executable_string.vader

@@ -33,7 +33,7 @@ Execute(It should be possible to compute an executable to check based on the res
   \ [{'status': 0, 'job_id': 'executable', 'command': 'foo'}],
   \ filter(copy(b:ale_history), 'v:val.job_id is# ''executable''')
 
-Execute(It handle the deferred command failing):
+Execute(We should handle the deferered executable command failing):
   let g:ale_emulate_job_failure = 1
 
   AssertLinter 0, 'echo'