gh-100176: venv: Remove redundant compat code for Python <= 3.2 (#100177)

gh-100176: Remove redundant compat code for Python 3.2 and older

Python 3.2 has been EOL since 2016-02-20 and 2.7 since 2020-01-01, so we
can remove this old compatibility check and unindent the old else-block.

Also, in the unindented block, replace a .format() call with an f-string.

Plus similar changes in the documentation.