Do not create a browser bound key when off the record. (2/2)

Before this change, while making SPC assertions when there was no pre
existing browser bound key (BBK), a new BBK is created in both regular
and off the record modes. After this change, in off the record mode the
BBK will not be created.

Browser bound keys are behind the flag
chrome://flags/#enable-secure-payment-confirmation-browser-bound-key.

Bug: 377278827, b:407760471
Change-Id: Iacb43cceecb57bc47e25bf0b87c328c73dc71d0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6576902
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Slobodan Pejic <slobodan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1465301}