Use explicit requirements from APEX

Previously, CAS APEX used ":sphal" and `android_load_sphal_library` to
open plugins from /vendor/lib/mediacas. It was a workaround because
there's no way to limit the scope to /vendor/lib/mediacas. And CAS
plugins are not SPHAL libraries.

Now, the APEX uses more explicit requirements: ":mediacas", which
limitss the scope to /vendor/lib/mediacas.

Bug: 298542407
Test: atest CtsMediaMiscTestCases:MediaCasTest
Change-Id: Id91a87e0f6ef8a761e37cabed7da8b9fed0591c2
diff --git a/cas/aidl/default/manifest.json b/cas/aidl/default/manifest.json
index 16b4f67..cdcecb2 100644
--- a/cas/aidl/default/manifest.json
+++ b/cas/aidl/default/manifest.json
@@ -1,9 +1,8 @@
 {
     "name": "com.android.hardware.cas",
     "version": 1,
-    // For CAS HAL to open plugins from /vendor/lib, "vendor" namespace should be imported.
-    // ":sphal" is an alias for the "vendor" namespace in Vendor APEX.
+    // For CAS HAL to open plugins from /vendor/lib/mediacas
     "requireNativeLibs": [
-        ":sphal"
+        ":mediacas"
     ]
 }