system/extras: remove BORINGSSL_201509 support.

The BORINGSSL_201509 define was used to make updating BoringSSL in
external/boringssl less painful. It allowed code to compile with either
the old BoringSSL (which didn't define BORINGSSL_201509) or with the new
(which does).

Now that the new version has landed, this change removes that support.

Change-Id: I19e661419f830459d015bf14e7905af2ec41b735
1 file changed