bug remove GCM collapse key

[jrconlin]

Closes #1149

[codecov-io]

Codecov Report

Merging #1150 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #1150    +/-   ##
=======================================
  Coverage     100%    100%            
=======================================
  Files          60      60            
  Lines        9938   10097   +159     
=======================================
+ Hits         9938   10097   +159

Impacted Files	Coverage Δ
autopush/router/gcm.py	100% <100%> (ø)	⬆️
autopush/router/gcmclient.py	100% <100%> (ø)	⬆️
autopush/tests/test_db.py	100% <0%> (ø)	⬆️
autopush/utils.py	100% <0%> (ø)	⬆️
autopush/db.py	100% <0%> (ø)	⬆️

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[bbangert]

Commit message is slightly off, missing the colon I think.