Remove zeros from build number

The zeros were kept in place of the timestamp in case people were
parsing it. Let's try to remove the zeros now and see what breaks.

Test: Presubmits
Change-Id: Ic52168f6be05a74323d8e47935de5c6a5cf15516

ui/build/build.go

@@ -79,7 +79,7 @@ func SetupOutDir(ctx Context, config Config) {
 		if username, ok = config.environ.Get("BUILD_USERNAME"); !ok {
 			ctx.Fatalln("Missing BUILD_USERNAME")
 		}
-		buildNumber = fmt.Sprintf("eng.%.6s.00000000.000000", username)
+		buildNumber = fmt.Sprintf("eng.%.6s", username)
 		writeValueIfChanged(ctx, config, config.OutDir(), "file_name_tag.txt", username)
 	}
 	// Write the build number to a file so it can be read back in