* Split to `subscribe_to_tzc` and `subscribe_to_zeph02`
* Add member function `subscribe_to` to `zephyr_account` to reduce comparisons
* Remove unused `galaxy` parameter
* Convert `while` to `for` around one of `subscribe_to` calls
Testing Done:
Compile only.
Reviewed at https://reviews.imfreedom.org/r/422/
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