Unneccesary declaration of `LA` variable in Practical 10

[sokimura39]

In the notebook for practical 10 where we assign a particular Borough to work with, the variable LA = 'Waltham Forest' is declared twice in sections 1.5.1 and 2.3. The latter needs to be dropped, since while changing the scope in the former declaration to a different borough is recommended, the latter impacts the title of the matplotlib plot which causes incorrect titles.