Move MetadataHeader to libui

To remove BufferHubMetadata off pdx dependency.

Note that the __attribute__(packed) is removed as part of this CL, as
it's not really needed and is triggering clang warnings.

Test: build passed. Not test needed as no behavior changes.
Bug: 118893702
Change-Id: Ifae94a143a2bedef68a653c57f089b95d166e6d7
diff --git a/libs/ui/tests/Android.bp b/libs/ui/tests/Android.bp
index 18bbb3e..ca73be7 100644
--- a/libs/ui/tests/Android.bp
+++ b/libs/ui/tests/Android.bp
@@ -73,10 +73,13 @@
 
 cc_test {
     name: "BufferHubMetadata_test",
-    header_libs: ["libbufferhub_headers", "libdvr_headers"],
+    header_libs: [
+        "libbufferhub_headers",
+        "libdvr_headers",
+        "libpdx_headers",
+    ],
     shared_libs: [
         "libbase",
-        "libpdx_default_transport",
         "libui",
         "libutils",
     ],