feat: Disabled MITx from program nudge emails

[irfanuddinahmad]

Description

This PR disables the program nudge emails for MITx

Supporting information

Exempt MIT courses from the send_program_course_nudge emails that are designed to go out to a learner after they have earned a passing grade in a course for 2 reasons:

1. Timing - these are being sent out before their course end dates have passed AND before certificate display availability dates have passed.
2. Inaccurate recommendations - one of their program series has a set sequence, and this nudge could recommended a course that is sequentially supposed to follow one more course.

As our nudge email is designed to look at the passed_timestamp and seemingly not much else, this overlooks important pieces like: has the course actually ended, has the assignment due date passed, have certificates been made available to learners in the course yet, is the learner in the course on the verified enrollment track in the course they just completed or are they an instructor or something else, etc.