[8u] [JFR] 8246310 : Clean commented-out code about ModuleEntry andPackageEntry in JFR

[Denghui Dong]

Hi,
Could I have a review of this small patch that deletes the commented-out code about ModuleEntry andPackageEntry in JFR.
Most of the deleted code is commented out, except 
```
<XmlType name="Package" parameterType="const PackageEntry*" fieldType="const PackageEntry*"/>
```
in metadata.xml.
PackageEntry doesn't exist in 8u, so it's safe to delete this line.

Bugs: https://bugs.openjdk.java.net/browse/JDK-8246310
Webrev: http://cr.openjdk.java.net/~ddong/8246310/webrev.00/
Testing: jdk/jfr, no extra failure

Thanks,
Denghui Dong