Remove unsafe reflection trying to access the modifiers field

[derklaro]

This is no longer possible in recent java versions as the modifier field is registered to the reflection filter and writes will always fail. For backwards compatibility the methods are still there but there are no more internal usages of them.

In FieldUtils we can just use the writeStaticField method as it will be able to write to final fields without removing the modifier.

(This change compiles correctly and all tests are passing, see #1510 why it's not compiling with GH actions 😄 )

[dmulloy2]

Does essentially removing this functionality impact older Java versions? Or is it essentially unused?

[derklaro]

Now it uses a the FieldAccessor class which then uses a Lookup which essentially bypasses all checks the jvm makes if a field is writeable or not. This functionality is the same for all java versions since 8, so I don't see the reason for it to break on older versions at all.