Since iOS 8/OS X 10.9, there is an easier way to do this with NSURLComponents.
NSURL *url = [NSURL URLWithString:@"http://hostname.com/path?key=value"];
NSURLComponents *urlComponents = [[NSURLComponents alloc] initWithURL:url resolvingAgainstBaseURL:NO];
urlComponents.query = nil; // Strip out query parameters.
NSLog(@"Result: %@", urlComponents.string); // Should print http://hostname.com/path