Remove + [GULAppEnvironmentUtil isIOS7OrHigher] in next major version

[ncooke3]

The minimum supported iOS version is great than 7.0 so the + [GULAppEnvironmentUtil isIOS7OrHigher] API can be removed.

GoogleUtilities/GoogleUtilities/Environment/Public/GoogleUtilities/GULAppEnvironmentUtil.h

Lines 45 to 47 in 68ea347

	/// @return Returns @YES when is run on iOS version greater or equal to 7.0
	+ (BOOL)isIOS7OrHigher DEPRECATED_MSG_ATTRIBUTE(
	"Always `YES` because only iOS 8 and higher supported. The method will be removed.");