Xcode: Do not require code signing for compiler id (#15214)

The approach in commit v3.1.0-rc1~1^2 (Xcode: Fix compiler id detection
when code signing is required, 2014-10-22) still requires a code signing
key when targeting a real device.  Instead set CODE_SIGNING_REQUIRED to
"NO" to tell Xcode not to sign at all.  Drop the corresponding setting
of the code signing identity.

Modules/CMakeDetermineCompilerId.cmake

@@ -270,11 +270,6 @@ Id flags: ${testflags}
     else()
       set(id_sdkroot "")
     endif()
-    if(CMAKE_XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY)
-      set(id_code_sign_identity "CODE_SIGN_IDENTITY = \"${CMAKE_XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY}\";")
-    else()
-      set(id_code_sign_identity "")
-    endif()
     if(NOT ${XCODE_VERSION} VERSION_LESS 3)
       set(v 3)
       set(ext xcodeproj)

Modules/CompilerId/Xcode-3.pbxproj.in

@@ -81,7 +81,7 @@
 			buildSettings = {
 				ARCHS = "$(ARCHS_STANDARD_32_BIT)";
 				ONLY_ACTIVE_ARCH = YES;
-				@id_code_sign_identity@
+				CODE_SIGNING_REQUIRED = NO;
 				CONFIGURATION_BUILD_DIR = "$(BUILD_DIR)";
 				SYMROOT = .;
 				@id_toolset@