Remove duplicate dependencies from dev-quickstart docs

Turns out certain versions of Ubuntu packages tox to use Python
3, which breaks installing MySQL-Python into 2.x virtualenvs.
Since we already have "pip install tox" in these docs, let's
stick with that method rather than depending on what distros do.

Also remove other packages from SUSE line that are
duplicated by the "pip install" line.

Change-Id: I472704ab879446586ec7fa7ecd79da4f7212b81d
Closes-Bug: 1399463
Merge "Remove duplicate dependencies from dev-quickstart docs"