Fix conflict with common zsh alias

oh-my-zsh common-aliases plugin defines `alias -g T='| tail'`, which causes an
error with the line `local T dir f`.

Making these lines more explicit resolves this issue, while also being clearer
that the intent is to clear out the local variables.

Bug: 169191000
Fix: 169191000
Test: source build/envsetup.sh; lunch <target>; m
Change-Id: Ief27aa3d9f541d0c39c6c11d7d771818d6493d31