Adjust note.sql schema to work on current MySQL

Remove alerts functionality

This was never used, and is in a broken state right now (references
an incorrect database schema).

It seems rather unlikely that this functionality i

Remove alerts functionality

This was never used, and is in a broken state right now (references
an incorrect database schema).

It seems rather unlikely that this functionality is going to be
finished at this point, so instead drop it entirely.

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Updated SQL schema for new votes table required for user notes voting features.

Update table structure
# Thanks Derick!

alerts table

no longer using 'removed' column to mark deletion

schema and notes for the note table