Remove doc-gitlab-com image, not used anymore

This was an image used for the custom generated docs site.
We've since migrated to Nanoc, so we no longer need that image.

.gitlab-ci.yml

@@ -35,7 +35,6 @@ ruby-2.3.3-golang-1.8-git-2.7-phantomjs-2.1-node-7.1-postgresql-9.6 test: *test_
 ruby-2.3.3-golang-1.8-git-2.7-chrome-60.0-node-7.1-postgresql-9.6 test: *test_build
 ruby-2.4.1-golang-1.8-git-2.7-phantomjs-2.1-node-7.1-postgresql-9.6 test: *test_build
 www-gitlab-com test: *test_build
-doc-gitlab-com test: *test_build
 gitlab-qa test: *test_build
 golang-1.5-git-2.8.4 test: *test_build
 golang-1.6-git-2.8.4 test: *test_build
@@ -58,7 +57,6 @@ ruby-2.3.3-golang-1.8-git-2.7-phantomjs-2.1-node-7.1-postgresql-9.6: *build_and_
 ruby-2.3.3-golang-1.8-git-2.7-chrome-60.0-node-7.1-postgresql-9.6: *build_and_deploy
 ruby-2.4.1-golang-1.8-git-2.7-phantomjs-2.1-node-7.1-postgresql-9.6: *build_and_deploy
 www-gitlab-com: *build_and_deploy
-doc-gitlab-com: *build_and_deploy
 gitlab-qa: *build_and_deploy
 golang-1.5-git-2.8.4: *build_and_deploy
 golang-1.6-git-2.8.4: *build_and_deploy

Dockerfile.doc-gitlab-com

@@ -1,12 +0,0 @@
-FROM ruby:2.3-slim
-
-ENV PACKAGES="git-core pandoc locales"
-
-ADD / /
-RUN /scripts/install-doc-gitlab-com
-
-# Set UTF-8 http://jaredmarkell.com/docker-and-locales/
-# Must be set after install-essentials is run
-ENV LANG en_US.UTF-8
-ENV LANGUAGE en_US:en
-ENV LC_ALL en_US.UTF-8

scripts/install-doc-gitlab-com

@@ -1,17 +0,0 @@
-#!/bin/bash
-
-set -xeo pipefail
-
-apt-get update
-apt-get install -yq --no-install-recommends \
-  $PACKAGES
-
-apt-get autoremove -yq
-
-# Set UTF-8
-echo "en_US.UTF-8 UTF-8" > /etc/locale.gen
-locale-gen
-update-locale LANG=en_US.UTF-8 LC_CTYPE=en_US.UTF-8 LC_ALL=en_US.UTF-8
-locale -a
-
-rm -rf /var/lib/apt/lists/*