Add build tag to omit grpc

This is needed so we can build the runc shim without grpc as a
transative dependency.
With this change the runc shim binary went from 14MB to 11MB.
The RSS from an idle shim went from about 17MB to 14MB (back around
where it was in in 1.7).

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

api/runtime/sandbox/v1/sandbox_grpc.pb.go

@@ -1,3 +1,5 @@
+//go:build !no_grpc
+
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
 // - protoc-gen-go-grpc v1.2.0

api/runtime/task/v3/shim_grpc.pb.go

@@ -1,3 +1,5 @@
+//go:build !no_grpc
+
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
 // - protoc-gen-go-grpc v1.2.0