RFR [9] 8133807: java.desktop docs: replace some invalid "@returns" tags

[Alexander Stepanov]

Hello,

Could you please review the following fix:
http://cr.openjdk.java.net/~avstepan/8133807/webrev.00
for
https://bugs.openjdk.java.net/browse/JDK-8133807

Just a minor cleanup for docs.

Thanks,
Alexander