Even if you remove the lock screen, you'll still be forced to manually log in every time your system starts. This can be resolved though, using much the same technique as in previous versions of Windows. Hold down the Windows key, press R, type in 'netplwiz' and press Enter to launch the User Accounts dialog. Clear the 'Users must enter a user name and password to use this computer' checkbox and click OK. Enter the user name and password of the account that you'd like to be logged in automatically, click OK then restart your computer for the changes to take effect. Windows 8 should now boot directly to the Start screen.
NOTE: The account you automatically log into will lose all Admin privileges.