docs(notification): remove invalid migration note

[tay1orjones]

Refs carbon-design-system/carbon#11172

Reported on slack, I missed a spot on the notification docs.

Changelog

Removed

• Remove docs stating the title and subtitle props have been removed, they were not removed in v11.

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[jnm2377]

@tay1orjones I thought we did remove them though? I remember having to migrate notifications bc those props no longer worked, and they had to be children going forward. Did we change that at some point?

Here's one example: carbon-design-system/carbon#10674

[tay1orjones]

@jnm2377 yeah it was a last-minute reversal before v11 dropped to add them back in: carbon-design-system/carbon#11022

[aledavila]

Lgtm