[TASK] TcaMigration: remove unused variable and fix typo

Remove unused array `$migrateFields` in `migrateRequestUpdate()`.
Fix a small typo in PHPDoc block.

Resolves: #79762
Releases: master
Change-Id: I0bb22b01c1d963ef3788bff9437343fc826861ff
Reviewed-on: https://review.typo3.org/51639


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Tested-by: Thomas Hohn <thomas@hohn.dk>
Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Helmut Hummel <typo3@helhum.io>
Tested-by: Helmut Hummel <typo3@helhum.io>