Add METADATA to system/core: Apache2+BSD=NOTICE

Remaining GPL is old and deprecated or optional.

Bug: 68860345
Bug: 69058154
Bug: 151953481

Test: no code changes

Change-Id: Ib75bd2fbcf3c96f62a03559c335d31352f06c641
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..d97975c
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,3 @@
+third_party {
+  license_type: NOTICE
+}