Remove gwtjsonrpc library dependency

We no longer use GWT at all so this dep is not really appropriate. All
necessary code has been copied into Gerrit core.

Change-Id: I5e81f0c8fc37710101395301706bc7c3e09eeaec

java/com/google/gerrit/json/BUILD

@@ -4,6 +4,5 @@ java_library(
     visibility = ["//visibility:public"],
     deps = [
         "//lib:gson",
-        "//lib:gwtjsonrpc",
     ],
 )