Turn off code signing by default

Code signature can be added after build with the following command line:
codesign --force --sign 76BB5ACAC44CA5EFA5F879434D157B81DA842CFB SDL2.framework/Versions/A

Xcode/SDL/SDL.xcodeproj/project.pbxproj

@@ -2782,7 +2782,6 @@
 		00CFA621106A567900758660 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "3rd Party Mac Developer Application";
 				DEPLOYMENT_POSTPROCESSING = YES;
 				GCC_ALTIVEC_EXTENSIONS = YES;
 				GCC_AUTO_VECTORIZATION = YES;
@@ -2800,8 +2799,6 @@
 			isa = XCBuildConfiguration;
 			buildSettings = {
 				CLANG_LINK_OBJC_RUNTIME = NO;
-				CODE_SIGN_IDENTITY = "Mac Developer";
-				"CODE_SIGN_IDENTITY[sdk=macosx*]" = "Mac Developer";
 				COMBINE_HIDPI_IMAGES = YES;
 				DYLIB_COMPATIBILITY_VERSION = 1.0.0;
 				DYLIB_CURRENT_VERSION = 5.0.0;
@@ -2837,8 +2834,6 @@
 		00CFA625106A567900758660 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "Mac Developer";
-				"CODE_SIGN_IDENTITY[sdk=macosx*]" = "Mac Developer";
 				PRODUCT_NAME = "Standard DMG";
 				PROVISIONING_PROFILE = "";
 			};
@@ -2847,7 +2842,6 @@
 		00CFA627106A568900758660 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "";
 				GCC_ALTIVEC_EXTENSIONS = YES;
 				GCC_AUTO_VECTORIZATION = YES;
 				GCC_ENABLE_SSE3_EXTENSIONS = YES;
@@ -2864,8 +2858,6 @@
 			isa = XCBuildConfiguration;
 			buildSettings = {
 				CLANG_LINK_OBJC_RUNTIME = NO;
-				CODE_SIGN_IDENTITY = "Mac Developer";
-				"CODE_SIGN_IDENTITY[sdk=macosx*]" = "Mac Developer";
 				COMBINE_HIDPI_IMAGES = YES;
 				DYLIB_COMPATIBILITY_VERSION = 1.0.0;
 				DYLIB_CURRENT_VERSION = 5.0.0;
@@ -2901,8 +2893,6 @@
 		00CFA62B106A568900758660 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
-				CODE_SIGN_IDENTITY = "Mac Developer";
-				"CODE_SIGN_IDENTITY[sdk=macosx*]" = "Mac Developer";
 				PRODUCT_NAME = "Standard DMG";
 				PROVISIONING_PROFILE = "";
 			};