Don't expose sourceMapSourceRoots argument to Gradle (JS)

Exposing this property causes IDEA to treat it as a free
command line argument, which is undesirable.
Support source roots via setting command line arguments inside
JS gradle task.

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSCompilerArguments.java

@@ -45,7 +45,6 @@ public class K2JSCompilerArguments extends CommonCompilerArguments {
     @Argument(value = "-source-map-prefix", description = "Prefix for paths in a source map")
     public String sourceMapPrefix;
 
-    @GradleOption(DefaultValues.StringNullDefault.class)
     @Argument(
             value = "-source-map-source-roots",
             valueDescription = "<path>",