Merge jdk.internal.misc.JavaSecurityAccess and jdk.internal.misc.JavaSecurityProtectionDomainAccess shared secrets

java.security.ProtectionDomain initializes two different 'shared secrets' interfaces when one should be enough [1].

Given that ProtectionDomain is loaded during the startup of the VM, removing one interface and its implementation will reduce the startup time a litlle and make the world better.

[1] http://hg.openjdk.java.net/jdk9/jdk9/jdk/file/589795e4cd38/src/java.base/share/classes/java/security/ProtectionDomain.java#l103