libssp: Download directory from gitlab instead of svn

svn is typically blocked on corporate firewalls.

Dockerfile.dev

@@ -2,7 +2,7 @@ FROM ubuntu:18.04
 
 RUN apt-get update -qq && apt-get install -qqy --no-install-recommends \
     git wget bzip2 file unzip libtool pkg-config cmake build-essential \
-    automake yasm gettext autopoint vim python ninja-build subversion \
+    automake yasm gettext autopoint vim python ninja-build \
     ca-certificates curl less && \
     apt-get clean -y && \
     rm -rf /var/lib/apt/lists/*