test-release.sh: Kill python2

Don't prefer python2's virtualenv when setting up the test-suite.
Always use python3 instead, since that's what we support everywhere else
anyway.

Differential Revision: https://reviews.llvm.org/D106941

llvm/utils/release/test-release.sh

@@ -508,11 +508,8 @@ fi
 # Setup the test-suite.  Do this early so we can catch failures before
 # we do the full 3 stage build.
 if [ $do_test_suite = "yes" ]; then
-  venv=virtualenv
-  if ! type -P 'virtualenv' > /dev/null 2>&1 ; then
-    check_program_exists 'python3'
-    venv="python3 -m venv"
-  fi
+  check_program_exists 'python3'
+  venv="python3 -m venv"
 
   SandboxDir="$BuildDir/sandbox"
   Lit=$SandboxDir/bin/lit