Update project.json to remove redundant System.Runtime dependency.

- This package is pulled in transitively.

src/Microsoft.AspNetCore.WebSockets.Protocol/project.json

@@ -17,7 +17,6 @@
         "System.IO": "4.1.0-*",
         "System.Linq": "4.0.1-*",
         "System.Net.WebSockets": "4.0.0-*",
-        "System.Runtime": "4.0.21-*",
         "System.Runtime.InteropServices": "4.0.21-*",
         "System.Runtime.Extensions": "4.1.0-*",
         "System.Security.Cryptography.Algorithms": "4.0.0-*",

src/Microsoft.AspNetCore.WebSockets.Server/project.json

@@ -18,7 +18,6 @@
     "net451": {},
     "dotnet5.4": {
       "dependencies": {
-        "System.Runtime": "4.0.21-*"
       }
     }
   }