Removed deprecated code marked in 5.0.x : oxUser::_checkLogin()

Removed function and tests, changed usages, updated oxInputValidator::checkLogin()
Removed deprecated code marked in 5.0.x : oxUser::_checkEmail()

Removed function and tests, changed usages.
Removed deprecated code marked in 5.0.x : oxUser::checkPassword()

Removed function and tests, changed usages.
Removed deprecated code marked in 5.0.x : oxUser::checkRequiredFields()

Removed function and tests, changed usages.
Removed deprecated code marked in 5.0.x : oxUser::checkCountries()

Removed function and tests, changed usages.
Removed deprecated code marked in 5.0.x : oxUser::_checkVatId()

Removed function and tests, changed usages.
Removed deprecated code marked in 5.0.x : oxUser::_checkRequiredArrayFields()

Removed function and tests, changed usages.
Removed deprecated code marked in 5.0.x : oxUser::checkPassword()

Fixing usages in account_password class and tests
Changing return type to correct class names.
Removed deprecated code marked in 5.0.x : oxUser::checkPassword()

Fixing usages in forgotpwd class and tests
Removed deprecated code marked in 5.0.x : oxUser::checkPassword()

Fixing usages in forgotpwd class and tests