Remove the OCR button and its feat_ocr toggle from the photo Properties
page. The feature moved to the pdf_cover_page plugin, which already owned
the pwg.pdfcp.ocrCover web service it called, so it now ships as one
self-contained unit instead of straddling two plugins.

Enable it there under Settings -> "Show the OCR button on the photo
properties page" (requires pdf_cover_page 16.7.0+). A stored feat_ocr
value is simply ignored from now on.

The shared .pp-cd-header/.pp-cd-actions CSS is kept: Title Case, Creation
date and Linked albums still use it.