Remove leptonica and cffi

docs/conf.py

@@ -91,11 +91,13 @@ if on_rtd:
         'pikepdf',
         'pikepdf.models',
         'pikepdf.models.metadata',
-        'ocrmypdf.leptonica',
     ]
     sys.modules.update((mod_name, Mock()) for mod_name in MOCK_MODULES)
 
-from importlib_metadata import version as package_version
+try:
+    from importlib_metadata import version as package_version
+except ModuleNotFoundError:
+    from importlib.metadata import version as package_version
 
 # The full version, including alpha/beta/rc tags.
 release = package_version('ocrmypdf')

docs/cookbook.rst

@@ -181,10 +181,7 @@ might remove desirable content, especially from poor quality scans.
    ignored. This should not be used on documents that contain color
    photos as it may remove them.
 -  ``--deskew`` will correct pages were scanned at a skewed angle by
-   rotating them back into place. Skew determination and correction is
-   performed using `Postl's variance of line
-   sums <http://www.leptonica.org/skew-measurement.html>`__ algorithm as
-   implemented in `Leptonica <http://www.leptonica.org/index.html>`__.
+   rotating them back into place.
 -  ``--clean`` uses
    `unpaper <https://www.flameeyes.eu/projects/unpaper>`__ to clean up
    pages before OCR, but does not alter the final output. This makes it

docs/installation.rst

@@ -189,7 +189,6 @@ of ocrmypdf, and install the following dependencies:
         liblept5 \
         libxml2 \
         pngquant \
-        python3-cffi \
         python3-distutils \
         python3-pkg-resources \
         python3-reportlab \
@@ -371,10 +370,8 @@ dependencies:
         ghostscript \
         icc-profiles-openicc \
         jbig2dec \
-        lib64leptonica5 \
         pngquant \
         python3-pip \
-        python3-cffi \
         python3-distutils-extra \
         python3-pkg-resources \
         python3-reportlab \