Remove unused or obsolete plugins

pica-etherpad/Dockerfile

@@ -37,14 +37,12 @@ RUN curl -SL https://github.com/ether/etherpad-lite/archive/${ETHERPAD_VERSION}.
         ep_align \
         ep_author_hover \
         ep_comments_page \
-        ep_countable \
         ep_delete_empty_pads \
         ep_font_color \
         ep_headings2 \
         ep_markdown \
         ep_pads_stats \
         ep_page_view \
-        ep_spellcheck \
         ep_subscript_and_superscript \
         ep_table_of_contents \
         ep_user_font_size && \