Cleanup BUILD.gn files from imports like foo:foo

Repalce all occurrences of foo:foo in deps with just foo in BUILD.gn
files.

Done with Sublime regex replace.
Find: \b([-a-zA-Z0-9_]+):+\1\b
In: *.gn
Replace with: \1

Bug: None
Change-Id: I40aba1b14face687a595b852ffe443cb20197611
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127899
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27225}

api/audio/BUILD.gn

@@ -59,7 +59,7 @@ rtc_source_set("aec3_config_json") {
     "../../rtc_base:rtc_base_approved",
     "../../rtc_base:rtc_json",
     "../../rtc_base/system:rtc_export",
-    "//third_party/abseil-cpp/absl/strings:strings",
+    "//third_party/abseil-cpp/absl/strings",
   ]
 }