Revert "Update includes for webrtc/{base => rtc_base} rename (2/3)"

This reverts commit c3771cc4d37f5573fe53b7c7cff295a4f0f9560f.
(breaks downstream internal project)

BUG=webrtc:7634
NOTRY=True
NOPRESUBMIT=True

Review-Url: https://codereview.webrtc.org/2972463002 .
Cr-Commit-Position: refs/heads/master@{#18873}

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCSSLAdapter.h

@@ -14,7 +14,7 @@
 
 /**
  * Initialize and clean up the SSL library. Failure is fatal. These call the
- * corresponding functions in webrtc/rtc_base/ssladapter.h.
+ * corresponding functions in webrtc/base/ssladapter.h.
  */
 RTC_EXTERN BOOL RTCInitializeSSL();
 RTC_EXTERN BOOL RTCCleanupSSL();