Get rid of coroutinesWarn/coroutinesEnable/coroutinesError

Use a single coroutinesState instead. Change the coroutines state in
some tests from "warn" to "enable"/"error" to test that deserialization
of older config files works ("warn" is the default value, so it wasn't
testing anything here)

compiler/testData/cli/js/jsExtraHelp.out

@@ -8,7 +8,8 @@ where advanced options include:
   -Xplugin=<path>            Load plugins from the given classpath
   -Xmulti-platform           Enable experimental language support for multi-platform projects
   -Xno-check-impl            Do not check presence of 'impl' modifier in multi-platform projects
-  -Xcoroutines={enable|warn|error} Enable coroutines or report warnings or errors on declarations and use sites of 'suspend' modifier
+  -Xcoroutines={enable|warn|error}
+                             Enable coroutines or report warnings or errors on declarations and use sites of 'suspend' modifier
 
 Advanced options are non-standard and may be changed or removed without any notice.
 OK