De-template parse_proguard_map
De-template parse_proguard_map

Summary:
The function parse_proguard_map does not need to be templated since
it is sufficient for it to take a std::istream

Reviewed By: bertmaher

Differential Revision: D3495442

fbshipit-source-id: d55e46e6d3f1b5f6610958b1ad3cdff358331964

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