Remove semi-circular dependency between core and util

Add the 'fake' dependency to grpc-netty instead of grpc-core.
grpc-okhttp already depends on grpc-util and probably would be fine
without round_robin on Android.

There's not actually a circular dependency, but some tools can't handle
the compile vs runtime distinction. Such tools are broken, but fixes
have been slow and this approach works with no real downfalls.

Works around #10576 #10701

core/build.gradle

@@ -19,8 +19,7 @@ description = 'gRPC: Core'
 dependencies {
     api project(':grpc-api')
     // force dependent jars to depend on latest grpc-context
-    runtimeOnly project(":grpc-context"),
-            project(":grpc-util")  // need grpc-util to pull in round robin
+    runtimeOnly project(":grpc-context")
     implementation libraries.gson,
             libraries.android.annotations,
             libraries.animalsniffer.annotations,

netty/build.gradle

@@ -28,6 +28,7 @@ dependencies {
             libraries.errorprone.annotations,
             libraries.perfmark.api,
             libraries.netty.unix.common
+    runtimeOnly project(":grpc-util")  // need grpc-util to pull in round robin
 
     // Tests depend on base class defined by core module.
     testImplementation testFixtures(project(':grpc-core')),