No implementation of signature `httpSetCredentialsAndKey`

[soumyaDghosh]

Describe the bug
The function httpSetCredentialsAndKey is defined in the header file with a signature, but there is no implementation of it in the library

To Reproduce
Steps to reproduce the behavior:

1. Go to https://github.com/OpenPrinting/libcups/blob/master/cups/http.h#L496
2. Look for its implementation in http.c or other files

Expected behavior
There should have been an implementation of httpSetCredentialsAndKey

System Information:
NA

[michaelrsweet]

This function was never implemented as you can't set the client certificate/key for a TLS connection after the negotiation. The correct API is actually cupsSetClientCredentials, which is implemented.

I will remove the erroneous prototype.

[michaelrsweet]

[master dcdf9fc] Remove bogus httpSetCredentialsAndKey prototype (Issue #114)