CertPrincipal: remove unused constructor

Change-Id: I4b845e32accdac8aaa701ab7143605fd6ecf6732
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4549947


Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: Matt Mueller <mattm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1147408}