[Cleanup] Add missing #include. Remove useless ones.

This CL is the result of running include-what-you-use tool on part
of the code base (audio target and dependencies) plus manual fixes.

bug: webrtc:8311
Change-Id: I277d281ce943c3ecc1bd45fd8d83055931743604
Reviewed-on: https://webrtc-review.googlesource.com/c/106280
Commit-Queue: Yves Gerey <yvesg@google.com>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25311}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 36e4f57..86bdf2b 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -285,6 +285,7 @@
   visibility = [ "*" ]
   libs = []
   deps = [
+    ":checks",
     ":criticalsection",
     ":macromagic",
     ":platform_thread_types",
@@ -370,6 +371,7 @@
   deps = [
     ":rtc_base_approved",
     "../system_wrappers",
+    "//third_party/abseil-cpp/absl/types:optional",
   ]
 }