Revert of Enable -Wdeprecated-register (except on CrOS).

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 113144be4f8ace4622615cfcbc5413bc30235f49..a4def5a766ee829190caf232a95036d13f06d081 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1064,6 +1064,11 @@
       # also contain a default: branch. Chrome is full of that.
       "-Wno-covered-switch-default",
 
+      # Clang considers the `register` keyword as deprecated, but e.g.
+      # code generated by flex (used in angle) contains that keyword.
+      # http://crbug.com/255186
+      "-Wno-deprecated-register",
+
       # TODO(thakis): This used to be implied by -Wno-unused-function,
       # which we no longer use. Check if it makes sense to remove
       # this as well. http://crbug.com/316352
@@ -1072,14 +1077,6 @@
       # TODO(hans): Get this cleaned up, http://crbug.com/428099
       "-Wno-inconsistent-missing-override",
     ]
-
-    if (is_chromeos) {
-      cflags += [
-        # TODO(thakis): Figure out why CrOS needs this, fix, remove.
-        # https://crbug.com/806812
-        "-Wno-deprecated-register",
-      ]
-    }
 
     # Chrome's hermetic Clang compiler, NaCl's Clang compiler and Xcode's Clang
     # compiler will almost always have different versions. Certain flags may not