Initial testing seems to show that jemalloc is a probable source of our
memory leaks with zuul-scheduler and zuul-web under python3.7 and
python3.8. While this was desireable under python3.5 with zuul-executor
it doesn't seem like we want to enable this universally. For this reason
remove jemalloc from the base image. It can be added into images in
specific places if desireable but isn't a good default.
Change-Id: I671eef4ef27fdde161b52cf0a4187fac10ac8c4e
e9854d8bdc