Move YamlUtils to be under google.registry.util package

This makes it simpler to package google.registry.util as a separate project in
Gradle that can be depended upon by the proxy package. Currently the proxy
package depends on both google.registry.util and google.registry.config.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=221450085

java/google/registry/config/BUILD

@@ -23,6 +23,5 @@ java_library(
         "@javax_inject",
         "@joda_time",
         "@org_joda_money",
-        "@org_yaml_snakeyaml",
     ],
 )