go.talks: remove redundant rules from app.yaml

LGTM=dsymonds
R=dsymonds
CC=golang-codereviews
https://golang.org/cl/94700047
diff --git a/app.yaml b/app.yaml
index 64fe368..d6ca711 100644
--- a/app.yaml
+++ b/app.yaml
@@ -12,4 +12,4 @@
 - url: /.*
   script: _go_app
 
-nobuild_files: ^((201[0-9]|pkg)/)
+nobuild_files: ^201[0-9]/