MDL-43532 Course: Remove deprecated functions from calendar

This function was deprecated in 2.4 and was due for removal in 2.6.

Removing as per deprecation policy.
MDL-43534 Course: Remove deprecated functions from course/renderer

This function was deprecated in 2.4 and was due for removal in 2.6.

Removing as per deprecation policy.
Merge branch 'MDL-43595-master' of git://github.com/damyon/moodle
Merge branch 'MDL-43532-master' of git://github.com/andrewnicols/moodle
Merge branch 'MDL-43534-master' of git://github.com/andrewnicols/moodle
MDL-33952 Assignment - bon voyage!

mod_assignment has been replaced with a stub that only exists to support restoring and
auto upgrading to mod_assign. If you require mod_assignment for some old plugin, then
overwrite with the 2.6 version manually.