Use google.api instead of custom googleapi package

Use the standard google.api package to not create conflicts with other
proto definition that uses the same package.

Change-Id: I264db977a2316ced0fdfb6ab8e499a1258726cb7
diff --git a/requirements.txt b/requirements.txt
index a09582f..d8950dd 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,3 +11,4 @@
 service_identity==18.1.0
 simplejson==3.16.0
 structlog~=19.1.0
+googleapis-common-protos~=1.51.0