update templates to not include runtime sections in project.json

src/csharp/Grpc.Examples/project.json

 {
   "buildOptions": {
   },
+  "runtimes": {
+    "win7-x64": { },
+    "debian.8-x64": { },
+    "osx.10.11-x64": { }
+  },
 
   "dependencies": {
     "Grpc.Core": {

templates/src/csharp/Grpc.Core/project.json.template

@@ -33,7 +33,7 @@
       "xmlDoc": true
     },
     "dependencies": {
-      "Ix-Async": "1.2.5"
+      "System.Interactive.Async": "3.0.0"
     },
     "frameworks": {
       "net45": { },

templates/src/csharp/Grpc.Examples.MathClient/project.json.template

 %YAML 1.2
 --- |
   {
-    <%include file="../build_options.include" args="executable=True"/>
+    <%include file="../build_options.include" args="executable=True,includeRuntimes=False"/>
     "dependencies": {
       "Grpc.Examples": {
         "target": "project"

templates/src/csharp/Grpc.Examples.MathServer/project.json.template

 %YAML 1.2
 --- |
   {
-    <%include file="../build_options.include" args="executable=True"/>
+    <%include file="../build_options.include" args="executable=True,includeRuntimes=False"/>
     "dependencies": {
       "Grpc.Examples": {
         "target": "project"

templates/src/csharp/Grpc.IntegrationTesting.QpsWorker/project.json.template

 %YAML 1.2
 --- |
   {
-    <%include file="../build_options.include" args="executable=True,includeData=True"/>
+    <%include file="../build_options.include" args="executable=True,includeData=True,includeRuntimes=False"/>
     "dependencies": {
       "Grpc.IntegrationTesting": {
         "target": "project"

templates/src/csharp/Grpc.IntegrationTesting.StressClient/project.json.template

 %YAML 1.2
 --- |
   {
-    <%include file="../build_options.include" args="executable=True,includeData=True"/>
+    <%include file="../build_options.include" args="executable=True,includeData=True,includeRuntimes=False"/>
     "dependencies": {
       "Grpc.IntegrationTesting": {
         "target": "project"

templates/src/csharp/build_options.include

-<%page args="executable=False,includeData=False"/>\
+<%page args="executable=False,includeData=False,includeRuntimes=True"/>\
 "buildOptions": {
   % if executable:
     "emitEntryPoint": true
@@ -51,6 +51,8 @@
       }
     }
   },
+  %endif
+  % if includeRuntimes:
   "runtimes": {
     "win7-x64": { },
     "debian.8-x64": { },