The OCR option for images and PDF files seems to be missing in the new Google Drive (the check box in the upload configuration is missing).
Is this option completely gone or did it just move elsewhere?
It has moved elsewhere. OCR is no longer performed during upload.
Instead, upload your files using "drag and drop", or the red "New" button (top-left of Google Drive Web UI). After uploading, right-click the file and choose "Open with" --> "Google Docs". Drive will convert the image to a Google Doc, and when you open the new converted file, the image will be at the top of the document and any OCR'd text will appear below (so be sure to scroll down in the converted document!).