Remove performance test

Making this an integration test ended up giving mixed results.
This test when run without the performance changes in this branch did
not reflect the performance gains seen when running pyenv-virtualenvs
outside of the test environment. The test was not accomplishing its goal.

test/virtualenvs.bats

@@ -81,31 +81,6 @@ OUT
   unstub pyenv-virtualenv-prefix
 }
 
-@test "list virtual environments performance" {
-  local count index start end elapsed max
-
-  count=180
-  max_duration=2
-
-  # Create venvs
-  for i in $(seq 1 $count); do
-    create_m_venv "3.14.3" "venv-${i}"
-  done
-
-  # List virtual environments and record the execution time.
-  # Run pyenv-virtualenvs without any flags because this is the most
-  # expensive operation.
-  start=$(date +%s)
-  run pyenv-virtualenvs
-  end=$(date +%s)
-  elapsed=$((end - start))
-
-  echo "# Listed $count venvs in ${elapsed}s." >&3
-
-  assert_success
-  assert [ "$elapsed" -le "$max_duration" ]
-}
-
 @test "list virtual environments with hit prefix" {
   stub pyenv-version-name ": echo 3.3.3/envs/venv33"
   stub pyenv-version-origin ": echo PYENV_VERSION"