Investigate if the `debug` or `spt` (singlePassType) params are used anywhere

[rcebulko]

The service has code to handle each, but neither is used in https://github.com/ampproject/amphtml/blob/master/src/error.js and AFAICT neither shows up in any of the logs.

/cc @jridgewell Are you familiar with these by chance?

[jridgewell]

/cc @erwinmombay

[erwinmombay]

Id like to leave spt for now in the code base, I'd like to use it to split the traffic for single pass and its myriads of obfuscation errors