Remove unused cube OCR engine modes (#1281)

Since commit cdc3533 Tesseract checks
the value passed for `--oem NUM`.

That only works as expected when the old (now unused) engine mode values
for cube are removed.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

ccstruct/publictypes.h

@@ -277,8 +277,6 @@ enum OcrEngineMode {
                                 // command-line configs, or if not specified
                                 // in any of the above should be set to the
                                 // default OEM_TESSERACT_ONLY.
-  OEM_CUBE_ONLY,                // Run Cube only - better accuracy, but slower
-  OEM_TESSERACT_CUBE_COMBINED,  // Run both and combine results - best accuracy
   OEM_COUNT			// Number of OEMs
 };