Delete Dockerfile.build

It was outdated

Dockerfile.build

@@ -1,10 +0,0 @@
-FROM ubuntu:16.04
-
-RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
-    emacs-nox \
-    build-essential \
-    libssl-dev sqlite3 \
-    libsqlite3-dev \
-    libevent-dev \
-    g++ \
-    libboost-dev