Disable save work btn and take "too many attempts" msg out of {% elif %}

Doing these because presently, if there's time remaining
after an exam submission, re-opening the exam shows a disabled submit
button but not disabled save answer button, and doesn't say anything
about why submissions are disabled.
Merge pull request #2100 from Stanford-Online/jbau-interstitial

Disable save work btn and take "too many attempts" msg out of {% elif %}