Remove remains of webrtc/base

All downstream code have been updated to the new location.

In PRESUBMIT.py:
* Remove webrtc/rtc_base from CPP_BLACKLIST
* Add webrtc/rtc_base to LEGACY_API_DIRS

Fix some duplicated paths in
webrtc/modules/audio_processing/test/conversational_speech/BUILD.gn

BUG=webrtc:7634
TBR=kwiberg@webrtc.org

Review-Url: https://codereview.webrtc.org/2976293002
Cr-Commit-Position: refs/heads/master@{#19094}
diff --git a/webrtc/api/BUILD.gn b/webrtc/api/BUILD.gn
index e87509b..7c43808 100644
--- a/webrtc/api/BUILD.gn
+++ b/webrtc/api/BUILD.gn
@@ -28,7 +28,7 @@
     ":audio_mixer_api",
     ":transport_api",
     "..:webrtc_common",
-    "../base:rtc_base_approved",
+    "../rtc_base:rtc_base_approved",
     "audio_codecs:audio_codecs_api",
   ]
 }
@@ -83,8 +83,8 @@
   deps = [
     ":rtc_stats_api",
     "..:webrtc_common",
-    "../base:rtc_base",
-    "../base:rtc_base_approved",
+    "../rtc_base:rtc_base",
+    "../rtc_base:rtc_base_approved",
     "audio_codecs:audio_codecs_api",
   ]
 
@@ -143,7 +143,7 @@
   ]
 
   deps = [
-    "../base:rtc_base_approved",
+    "../rtc_base:rtc_base_approved",
   ]
 }
 
@@ -153,8 +153,8 @@
   ]
 
   deps = [
-    "../base:rtc_base_approved",
     "../modules:module_api",
+    "../rtc_base:rtc_base_approved",
   ]
 }
 
@@ -178,7 +178,7 @@
   ]
 
   deps = [
-    "../base:rtc_base_approved",
+    "../rtc_base:rtc_base_approved",
     "../system_wrappers",
   ]
 
@@ -206,7 +206,7 @@
   ]
 
   deps = [
-    "../base:rtc_base_approved",
+    "../rtc_base:rtc_base_approved",
   ]
 }
 
@@ -235,7 +235,7 @@
     ]
     deps = [
       ":libjingle_peerconnection_api",
-      "../base:rtc_base_approved",
+      "../rtc_base:rtc_base_approved",
     ]
     if (!build_with_chromium && is_clang) {
       # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).