Clean up resources shared between x-pack core and security

[jaymode]

There are a large number of certificates that we have checked in as test resources. Both the x-pack core and security projects have the same paths and many of the same names for certificates and keystores. However, the content has diverged in some of the files. This would be fine if the projects were completely separated but as it stands the core resources are copied into the security source set for tests. This can lead to confusing failures if you are not aware of this and do not know which file is actually being used, which happened to me while working on cipher changes for JDK 11.

We should either remove the sharing of these resources or only keep them in core so that we do not have this situation where files diverge and we're unsure of which files are being used.

[elasticmachine]

Pinging @elastic/es-security