Remove HAVE_SRTP define and unmaintained code.

webrtc/pc/externalhmac.cc

Index: webrtc/pc/externalhmac.cc
diff --git a/webrtc/pc/externalhmac.cc b/webrtc/pc/externalhmac.cc
index 2d3ff5f873de4d18c84b1b345591faa855787f82..94e39d30b77e02ad206c4b56ae21e724f15cfe2c 100644
--- a/webrtc/pc/externalhmac.cc
+++ b/webrtc/pc/externalhmac.cc
@@ -14,12 +14,8 @@
 
 #include "webrtc/base/logging.h"
 
-#ifdef HAVE_SRTP
 #include "third_party/libsrtp/crypto/include/crypto_kernel.h"
 #include "third_party/libsrtp/include/srtp.h"
-#endif // HAVE_SRTP
-
-#if defined(HAVE_SRTP)
 
 // Begin test case 0 */
 static const uint8_t kExternalHmacTestCase0Key[20] = {
@@ -150,5 +146,3 @@ srtp_err_status_t external_crypto_init() {
   }
   return srtp_err_status_ok;
 }
-
-#endif  // defined(HAVE_SRTP)