Rollup merge of #81954 - joshtriplett:release-notes-group-platform-notes, r=XAMPPRocky
Rollup merge of #81954 - joshtriplett:release-notes-group-platform-notes, r=XAMPPRocky

RELEASES.md 1.50: Group platform support notes together

Move the note about dropping cloudabi next to the other platform support
changes.

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust