Revert "Adding absl includes and defines to rtc_* templates."

This reverts commit 9d8f3850f4c4faad5dc5ab32ab6f2c9c43df7b6c.

Reason for revert: Breaks some trybots: https://build.chromium.org/p/client.webrtc/builders/iOS64%20Release/builds/12793.

Original change's description:
> Adding absl includes and defines to rtc_* templates.
> 
> This CL implicitly adds the -I compiler flag and absl macros to WebRTC
> templates. In order to include absl headers using relative paths, WebRTC
> needs to ensure that all its build targets are able to see absl headers.
> 
> This can also be done with public_deps, but WebRTC is trying to avoid
> it because it creates problems with other build systems. Given this
> constraint, using rtc_* templates is the most reliable solution.
> 
> Please note that rtc_* templates are adding absl includes and defines
> as public_configs, this means that build targets with WebRTC targets
> in their public_deps will propagate these configs following the GN
> guideline.
> 
> Bug: webrtc:8821
> Change-Id: I4aa594a524f4bd045bcb3e80d76cc27f06fe01d7
> Reviewed-on: https://webrtc-review.googlesource.com/70367
> Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#22927}

TBR=phoglund@webrtc.org,mbonadei@webrtc.org

Change-Id: Id8e1f881c57553386566eb1970f6b9f8632cab37
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8821
Reviewed-on: https://webrtc-review.googlesource.com/71000
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22928}
diff --git a/webrtc.gni b/webrtc.gni
index 66f8b11..cfc9cb0 100644
--- a/webrtc.gni
+++ b/webrtc.gni
@@ -278,9 +278,6 @@
   webrtc_default_visibility += [ webrtc_root + "/../webrtc_overrides/*" ]
 }
 
-absl_include_config = "//third_party/abseil-cpp:absl_include_config"
-absl_define_config = "//third_party/abseil-cpp:absl_define_config"
-
 template("rtc_test") {
   test(target_name) {
     forward_variables_from(invoker,
@@ -299,11 +296,7 @@
     configs += invoker.configs
     configs -= rtc_remove_configs
     configs -= invoker.suppressed_configs
-    public_configs = [
-      rtc_common_inherited_config,
-      absl_include_config,
-      absl_define_config,
-    ]
+    public_configs = [ rtc_common_inherited_config ]
     if (defined(invoker.public_configs)) {
       public_configs += invoker.public_configs
     }
@@ -331,11 +324,7 @@
     configs += invoker.configs
     configs -= rtc_remove_configs
     configs -= invoker.suppressed_configs
-    public_configs = [
-      rtc_common_inherited_config,
-      absl_include_config,
-      absl_define_config,
-    ]
+    public_configs = [ rtc_common_inherited_config ]
     if (defined(invoker.public_configs)) {
       public_configs += invoker.public_configs
     }
@@ -365,11 +354,7 @@
     ]
     deps += invoker.deps
 
-    public_configs = [
-      rtc_common_inherited_config,
-      absl_include_config,
-      absl_define_config,
-    ]
+    public_configs = [ rtc_common_inherited_config ]
     if (defined(invoker.public_configs)) {
       public_configs += invoker.public_configs
     }
@@ -393,11 +378,7 @@
     configs += invoker.configs
     configs -= rtc_remove_configs
     configs -= invoker.suppressed_configs
-    public_configs = [
-      rtc_common_inherited_config,
-      absl_include_config,
-      absl_define_config,
-    ]
+    public_configs = [ rtc_common_inherited_config ]
     if (defined(invoker.public_configs)) {
       public_configs += invoker.public_configs
     }
@@ -421,11 +402,7 @@
     configs += invoker.configs
     configs -= rtc_remove_configs
     configs -= invoker.suppressed_configs
-    public_configs = [
-      rtc_common_inherited_config,
-      absl_include_config,
-      absl_define_config,
-    ]
+    public_configs = [ rtc_common_inherited_config ]
     if (defined(invoker.public_configs)) {
       public_configs += invoker.public_configs
     }