Remove "Invitation Letter" and "Referrals" from Preferences Sidebar

[hokienick]

We aren't sure where these options came from, nevertheless there are dead links in these 2 sections. Please remove them from the sidebar.

[sandhiyakavi]

Tested in Test Environment. Invitation letter and Referrals are removed.

[sandhiyakavi]

cc: @SathyaJayabal

[Jobee1]

Tested in Beta environment, Working as expected.