Remove poppler (#393)

Leftover after #42

Author: stchris

Dockerfile

@@ -24,8 +24,7 @@ RUN apt-get -qq -y update \
     imagemagick-common imagemagick mdbtools djvulibre-bin \
     libtiff5-dev libjpeg-dev libfreetype6-dev libwebp-dev \
     libtiff-tools ghostscript librsvg2-bin jbig2dec \
-    # pdf processing toolkit
-    poppler-utils poppler-data pst-utils \
+    pst-utils \
     ### tesseract 
     tesseract-ocr-eng \
     tesseract-ocr-swa \