What's up with the note I found with Mazzy Fentan? Does it have anything to do with the ranger stronghold quest or is it just a useless note I found? I've looked all over the outside of the temple ruins and found nothing.

its to tell you where Mazzy is just read it and put it somewhere in your stronghold with Nebs head and Bohdis heart.

Nebs head and yoshis heart arent useless Jon:
Nebs head to the government for a reward
yoshis heart to Lathander temple

Where's the first half of the note? and I rather liked the taste of bohdi's heart

You sure it is Yosh's heart in lathandar's temple. I have it as Ilmater's temple, as he told me before dying

Oh forgot about the topic. Yes, if the note you are talking about is the one you found in the ranger cabin, then yes it's just letting you know where Mazzy is, You can pretty much be rid of it. However, if that is the second half of the journal page you found in the cell next to Mazzy's cell, then I do believe it is for the ranger, telling of a hidden cache.