all calls to should_defalate are passing wrong argument

[wnorris]

All of the calls to WP_Http_Encoding::should_decode() are passing the argument $theHeaders (or whatever that variable is named for that function. btw, why is it so inconsistent?). This array contains two keys 'headers' and 'cookies'. should_decode() is expecting only the 'headers' array, so every call to should_decode needs to be updated to pass $theHeaders['headers']. Otherwise, HTTP responses are never decompressed.

(In [11236]) Pass just the headers array to should_decode. Fixes #9754 props willnorris.