Add 'REMOVED' EnrolmentState to the Eligible Mentor States

[Piumal1999]

Is your feature request related to a problem? Please describe.
Mentees can have the REMOVED enrolment state. So admins should be able to change the mentor's state to REMOVED state

Describe the solution you'd like
Add REMOVED enrolment state to eligibleEnrolmentStatesForMentors list in src/main/java/org/sefglobal/scholarx/service/MentorService.java

Describe alternatives you've considered
N/A

Additional context
N/A

[Madhawa97]

Can you assign me?