PDF OCR: Update one metric to use whether OCR is actually available

This CL updates `RecordPDFOpenedWithA11yFeatureWithPdfOcr()` to record
the Accessibility.PDF.OpenedWith*.PdfOcr metrics with the information
about whether the OCR model is actually initialized.

OBSOLETE_HISTOGRAMS=Patterned histogram Accessibility.PDF.OpenedWith{A11yFeature}.PdfOcr is replaced by Accessibility.PDF.OpenedWith{A11yFeature}.PdfOcr2

AX-Relnotes: n/a.
Bug: 40912114
Test: out/Debug/browser_tests --gtest_filter=*PdfOcrUmaTest*
Change-Id: I0ee6bc381ab67bff6ba30db5973e6fbb92eb399f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5689764
Reviewed-by: Mark Schillaci <mschillaci@google.com>
Reviewed-by: Abigail Klein <abigailbklein@google.com>
Reviewed-by: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Andy Phan <andyphan@chromium.org>
Reviewed-by: Ramin Halavati <rhalavati@chromium.org>
Commit-Queue: Kyungjun Lee <kyungjunlee@google.com>
Cr-Commit-Position: refs/heads/main@{#1328539}