Explicitly exclude com.android.server from docs

With the move to OpenJDK 9 the packages under
com.android are not automatically hidden. There's
only two which show up, one of which
(com.android.internal.util) was already present.
com.android.server can just be explicitly hidden.

Test: make docs / diff
Bug: 69736344
Bug: 69736236
Change-Id: I44fb16e86a8d87152eba4e53a7b2d2290662bb63

Android.mk

@@ -1029,6 +1029,7 @@ framework_docs_LOCAL_DROIDDOC_OPTIONS := \
     -manifest ./frameworks/base/core/res/AndroidManifest.xml \
     -hidePackage com.android.okhttp \
     -hidePackage com.android.org.conscrypt \
+    -hidePackage com.android.server \
     -since $(SRC_API_DIR)/1.xml 1 \
     -since $(SRC_API_DIR)/2.xml 2 \
     -since $(SRC_API_DIR)/3.xml 3 \