Remove unused line from mac wheel builder (#3619)

diff --git a/.jenkins/mac-wheel.sh b/.jenkins/mac-wheel.sh
index 7d4a72c..0db7a7b 100644
--- a/.jenkins/mac-wheel.sh
+++ b/.jenkins/mac-wheel.sh
@@ -9,7 +9,6 @@
 # pyenv is nothing but trouble with non-interactive shells so we can't
 # eval "$(pyenv init -)"
 export PATH="/Users/jenkins/.pyenv/shims:${PATH}"
-export PYENV_SHELL=bash
 
 # TODO: upgrade wheel builder VM and run it on El Cap with python.org Pythons.
 if [[ "${label}" == "10.10" ]]; then