Rip out PPNS

[rogerhu]

I think this change will not really have any major objections.

PPNS - https://github.com/ParsePlatform/parse-server/wiki/PPNS-Protocol-Specification

#572
parse-community/parse-server#1113

References to PPNS: https://github.com/ParsePlatform/Parse-SDK-Android/search?utf8=%E2%9C%93&q=ppns

• Kill PPNSUtil.java
• Remove references in GCMRegistar.java

[jeacott1]

we are supporting ppns, so please dont 'rip it out!!'
jars will be made available shortly.

[rogerhu]

Could you elaborate? parse-community/parse-server#1113

[jeacott1]

our parse server offering (can I say which one?) supports PPNS, and as such we rely on the hook for the ppns extension jar.
it would be nice if this extension mechanism was more general, but as it is, its at least functional for us.

our PPNS implementation is not nodejs, and is not a trivial deploy, so as it stands, it wont be offered as open source. if however there was enough demand expressed we might be persuaded to offer a version that could be run as part of the OSS stack.

[natario1]

Done in #732