Remove uneeded dependencies for AppImage building

Pillow 0.7+ no longer requires separate installation of libraries like
libjpeg, zlib, etc, for common desktop architectures at least
(which is why we keep them in the INSTALL.md manual install commands).

TODO.md

@@ -207,8 +207,6 @@
 
 - Use Qt 5.14 for AppImage
 - Add AppImage & Flatpak metadata file
-- Pillow now bundle image libraries?
-  Update AppImage building script and INSTALL.md
 - Publish on Flathub and AppImageHub
 
 - Update to Mistune v2.0 when released

packaging/appimage/build.sh

@@ -42,10 +42,9 @@ install_apt_packages() {
         qt512imageformats qt512quickcontrols2 qt512svg \
         zip git wget cmake ccache \
         build-essential mesa-common-dev libglu1-mesa-dev freeglut3-dev \
-        libglfw3-dev libgles2-mesa-dev libjpeg-turbo8-dev zlib1g-dev \
-        libtiff5-dev liblcms2-dev libwebp-dev  libopenjp2-7-dev libssl-dev \
+        libglfw3-dev libgles2-mesa-dev libssl-dev \
         python3-dev python3-setuptools python3-pip libgdbm-dev libc6-dev \
-        zlib1g-dev libsqlite3-dev libffi-dev openssl libreadline-dev \
+        libsqlite3-dev libffi-dev openssl libreadline-dev \
         desktop-file-utils  # for appimage-lint.sh
 
     /usr/sbin/update-ccache-symlinks