Backlog: Use ISO-8859-1 encoding in System test compilation tasks

Using `ISO-8859-1` encoding value for the system test compilation tasks allows system tests to be compiled without having the[ step to copy gitattributes.zos](https://github.com/AdoptOpenJDK/openjdk-tests/blob/70992eb16fe5881e44a43f569fb9a5168bd5318b/system/common.xml#L63) properties files in the common.xml script.

We should get rid of the copy steps from the common.xml and update all the build files in openjdk-systemtest openj9-systemtest and stf repos to use `ISO-8859-1` as compilation encoding.

This will mean we will also no longer require to set the `src-encoding` property in [top.xml ](https://github.com/AdoptOpenJDK/stf/blob/f7d33b5261489635dee9b7df24600dd10f7229d4/stf.build/include/top.xml#L369)