build: tox understands "pypy38" on its own

Author: nedbat

tox.ini

@@ -51,22 +51,6 @@ commands =
 # For running against my own builds of CPython, or any other specific Python.
 basepython = {env:COVERAGE_ANYPY}
 
-[testenv:pypy37]
-basepython = pypy3.7
-
-[testenv:pypy38]
-basepython = pypy3.8
-
-[testenv:pypy37-rc]
-basepython = /usr/local/pypy/pypy3.7-v7.3.8rc1-osx64/bin/pypy3
-
-[testenv:pypy38-rc]
-basepython = /usr/local/pypy/pypy3.8-v7.3.8rc1-osx64/bin/pypy3
-
-[testenv:pypy39-rc]
-basepython = /usr/local/pypy/pypy3.9-v7.3.8rc1-osx64/bin/pypy3
-
-
 [testenv:doc]
 # Build the docs so we know if they are successful.  We build twice: once with
 # -q to get all warnings, and once with -QW to get a success/fail status