Fix complaints about mismatched new/delete

new[] should only pair with delete[]. Our tooling complained about the
`delete`s on lines 308, 387, and 397. The other cleanups are just
things I noticed while glancing around.

Bug: None
Test: Treehugger
Change-Id: I523f7eff21ab1d741322750f0be94fca26d2f4c5