Rename C bindings flags

This CL updates the C bindings flags based on changes to fidlc in
I89cebe6b5ce6a16a381afde294cf7636010038f8. All the C bindings flags now
start with "--deprecated-fuchsia-only-".

Change-Id: I26ac2281971b9c8a6d745685a9d81013a585bf80
Reviewed-on: https://fuchsia-review.googlesource.com/c/fidlbolt/+/534241
Reviewed-by: Felix Zhu <fcz@google.com>
diff --git a/backend/server.go b/backend/server.go
index 9348e43..4369d2f 100644
--- a/backend/server.go
+++ b/backend/server.go
@@ -438,11 +438,11 @@
 	case C:
 		switch r.Options.File {
 		case "header":
-			return fidlc("--c-header", "/dev/stdout")
+			return fidlc("--deprecated-fuchsia-only-c-header", "/dev/stdout")
 		case "client":
-			return fidlc("--c-client", "/dev/stdout")
+			return fidlc("--deprecated-fuchsia-only-c-client", "/dev/stdout")
 		case "server":
-			return fidlc("--c-server", "/dev/stdout")
+			return fidlc("--deprecated-fuchsia-only-c-server", "/dev/stdout")
 		default:
 			return response{}, fmt.Errorf("invalid file: %q", r.Options.File)
 		}