Hide com.android.server package with @hide javadoc tag

Metalava currently doesn't respect @Hide annoation in package statement.
Use the old @hide javadoc tag there temporarily until the problem is
fixed.

Bug: 146466118
Test: m
Test: m after adding
@SystemApi(client=MODULE_LIBRARIES,client=SYSTEM_SERVER) to some of the
classes under frameworks/base/services

Change-Id: I4af7380917fd2808bd6774b86fd4991485d6bfc6