install: drop Ubuntu 14.04 steps

Bit rot must have set in.

docs/installation.rst

@@ -269,68 +269,6 @@ environment variable contains ``$HOME/.local/bin``.
 
 To add JBIG2 encoding, see :ref:`jbig2`.
 
-Ubuntu 14.04 LTS
-----------------
-
-Installing on Ubuntu 14.04 LTS (trusty) is more difficult than some
-other options, because of its age. Several backports are required. For
-explanations of some steps of this procedure, see the similar steps for
-Ubuntu 16.04.
-
-Install system dependencies:
-
-.. code-block:: bash
-
-    sudo apt-get update
-    sudo apt-get install \
-        software-properties-common python-software-properties \
-        zlib1g-dev \
-        libexempi3 \
-        libjpeg-dev \
-        libffi-dev \
-        pngquant \
-        qpdf
-
-We will need backports of Ghostscript 9.16, libav-11 (for unpaper 6.1),
-Tesseract 4.00 (alpha), and Python 3.6. This will replace Ghostscript
-and Tesseract 3.x on your system. Python 3.6 will be installed alongside
-the system Python 3.4.
-
-If you prefer to not modify your system in this matter, consider using a
-Docker container.
-
-.. code-block:: bash
-
-    sudo add-apt-repository ppa:vshn/ghostscript -y
-    sudo add-apt-repository ppa:heyarje/libav-11 -y
-    sudo add-apt-repository ppa:alex-p/tesseract-ocr -y
-    sudo add-apt-repository ppa:jonathonf/python-3.6 -y
-
-    sudo apt-get update
-
-    sudo apt-get install \
-        python3.6-dev \
-        ghostscript \
-        tesseract-ocr \
-        tesseract-ocr-eng \
-        libavformat56 libavcodec56 libavutil54 \
-        wget
-
-Now we need to install ``pip`` and let it install ocrmypdf:
-
-.. code-block:: bash
-
-    curl https://bootstrap.pypa.io/ez_setup.py -o - | python3.6 && python3.6 -m easy_install pip
-    pip3.6 install ocrmypdf
-
-The optional dependency ``unpaper`` is only available at 0.4.2 in Ubuntu 14.04,
-and no backports are available. Previously the author maintained a backported
-.deb package for unpaper 6.1, but since Ubuntu 14.04 is now end of life, this is
-not supported. As such, ``unpaper`` is not available on Ubuntu 14.04 or must by
-compiled by hand.
-
-To add JBIG2 encoding, see :ref:`jbig2`.
-
 Arch Linux (AUR)
 ----------------