[Keymaster@ehi-kioya]

Quick follow up.

Since you’re using the add_filter() function, the anonymous function technique I mentioned above may not even be necessary (even though it should totally work).

An old-school named function like this should also accomplish the same goal:

function remove_login_errors( $error ) {
    return 'Error: Incorrect login details. Try again';
}
add_filter( 'login_errors', 'remove_login_errors' );

In any case, create_function() should still be avoided.

I think using anonymous functions as replacements for create_function() became popular because developers wanted a one line replacement for a bad one line piece of code.