How to log in to site after removing login form
Best bet is to reset the default theme to Bartik or one of the other core themes to log in, then you can fix your mistake there.

Using Drush:

drush vset theme_default bartik


Not using Drush:

Look in your variables table and switch out whatever is currently in theme_default for bartik (ensure that the number following from s: matches the number of letters in the theme name, so Bartik would be 6, Garland would be 7) 

UPDATE variable SET value='s:6:"bartik"' WHERE name = 'theme_default';
TRUNCATE cache;


(Modified from Unusable theme - How To reset your theme)