Remove unnecessary opencensus dep

The opencensus-java runtime dep was made purely optional for the core
grpc lib. This is reflected in the current bazel/gradle build, but not
yet in soong. Remove the `libs` dependency from the
grpc-java-core-internal target to fix this.

Bug: 361420649
Test: m
Change-Id: I27fdec733289b7bb398528439a05c4e35887deaa
diff --git a/core/Android.bp b/core/Android.bp
index f804f54..277953f 100644
--- a/core/Android.bp
+++ b/core/Android.bp
@@ -92,8 +92,6 @@
         "gson",
         "error_prone_annotations",
         "guava",
-        "opencensus-java-api",
-        "opencensus-java-contrib-grpc-metrics",
         "perfmark-api-lib",
     ],
     target: {