Remove GN GYP generator.

tools/gn/variables.h

Index: tools/gn/variables.h
diff --git a/tools/gn/variables.h b/tools/gn/variables.h
index 94208dbdd041ad27dee2219db64ca5b631fb6e62..85fbb96d34d49c836bd1f7f85c6b846d487f1a9e 100644
--- a/tools/gn/variables.h
+++ b/tools/gn/variables.h
@@ -123,22 +123,10 @@ extern const char kDirectDependentConfigs[];
 extern const char kDirectDependentConfigs_HelpShort[];
 extern const char kDirectDependentConfigs_Help[];
 
-extern const char kExternal[];
-extern const char kExternal_HelpShort[];
-extern const char kExternal_Help[];
-
 extern const char kForwardDependentConfigsFrom[];
 extern const char kForwardDependentConfigsFrom_HelpShort[];
 extern const char kForwardDependentConfigsFrom_Help[];
 
-extern const char kGypFile[];
-extern const char kGypFile_HelpShort[];
-extern const char kGypFile_Help[];
-
-extern const char kGypHeader[];
-extern const char kGypHeader_HelpShort[];
-extern const char kGypHeader_Help[];
-
 extern const char kHardDep[];
 extern const char kHardDep_HelpShort[];
 extern const char kHardDep_Help[];