Revert of Define MOJO_SHELL_CLIENT uniformly across content

content/public/common/BUILD.gn

Index: content/public/common/BUILD.gn
diff --git a/content/public/common/BUILD.gn b/content/public/common/BUILD.gn
index 9c1e0f771d49464b6f302489b4f81735726a644a..63f5fa9fff551becc2c58365799a039a5d6d9e6a 100644
--- a/content/public/common/BUILD.gn
+++ b/content/public/common/BUILD.gn
@@ -42,15 +42,6 @@
 # component export flags won't be consistent.
 config("static_switches_defines") {
   defines = [ "COMPILE_CONTENT_STATICALLY" ]
-}
-
-# Set in GN builds, triggering behavior in content when run from an external
-# Mojo shell.
-config("mojo_shell_client") {
-  # This configuration has only been tested on these platforms.
-  if (is_win || is_linux || is_chromeos) {
-    defines = [ "MOJO_SHELL_CLIENT" ]
-  }
 }
 
 # This target allows you to use the content_switches constants and statically