Remove 'schedule' field for projects

[jaragunde]

This is part of a feature present in phpreport 1.x that was never ported to 2.x. Other supporting code for that feature was removed in commits 395911eeddf8cb084418c7586838508d51ce0ea3 and 3a213b5003b12adc7c3af6629f3417efdc2bf697.

The field doesn't even work properly, its value can be saved but it's cleared when you edit a project.

[dmtrek14]

Related to #416