gh-112431: Unconditionally call `hash -r` (GH-112432)

gh-112431: Unconditionally call `hash -r` (GH-112432)

The `activate` script calls `hash -r` in two places to make sure the shell picks
up the environment changes the script makes. Before that, it checks to
see if the shell running the script is bash or zsh.

`hash -r` is specified by POSIX and is not exclusive to bash and zsh.
This guard prevents the script from calling `hash -r` in other
`#!/bin/sh`-compatible shells like dash.