fix: better package-info support

[nitram84]

When I filed #1967 I had only one sample app. With https://apkpure.com/who-becomes-rich/de.sellfisch.android.wwr/download/1.15.1 I found another app with package-infos e.g. javax.annotation.package-info. This time a package-info is just an interface, nothing else. I removed some checks to support this case too.

[skylot]

I think just checking for name package-info is enough. Access flags or even class type is not specified in java docs, so we can't rely on them (package info only mentioned in JLS here)
As a guard from protectors, we can also check that there are no fields and methods in that 'class'.

[skylot]

@nitram84 thanks 👍