Delete more unused corpus test expectations

Gets rid of more unused corpus text expectations. This change removes
expectations that are redundant because they contain exactly the same
pixels as another expectation.

Bug: pdfium:1987
Change-Id: Ic29ce992930013c2a3606e3a51891b48651ff5c7
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium_tests/+/103751
Reviewed-by: Nigi <nigi@chromium.org>
22 files changed