Remove redundant packages and move database specific ones to the db setup

* build-essential requires make, gcc
* remove libmysql++-dev: the mysql2 gem only requires libmysqlclient-dev
* remove postgresql-server-dev-9.1: the pg gem only requires libpq-dev
* replace python-dev, python-pip with python2.7: the pygments.rb gem only requires python2.7

doc/install/databases.md

@@ -35,7 +35,7 @@ GitLab supports the following databases:
 ## PostgreSQL
 
     # Install the database packages
-    sudo apt-get install -y postgresql-9.1 postgresql-server-dev-9.1
+    sudo apt-get install -y postgresql-9.1 libpq-dev
 
     # Install only the necessary gems
     sudo -u gitlab -H bundle install --deployment --without development test mysql

doc/install/installation.md

@@ -44,7 +44,7 @@ Now install the required packages:
     sudo apt-get update
     sudo apt-get upgrade
 
-    sudo apt-get install -y wget curl gcc checkinstall libxml2-dev libxslt-dev libcurl4-openssl-dev libreadline6-dev libc6-dev libssl-dev libmysql++-dev make build-essential zlib1g-dev libicu-dev redis-server openssh-server git-core python-dev python-pip libyaml-dev postfix libpq-dev
+    sudo apt-get install -y wget curl build-essential checkinstall libxml2-dev libxslt-dev libcurl4-openssl-dev libreadline6-dev libc6-dev libssl-dev zlib1g-dev libicu-dev redis-server openssh-server git-core python2.7 libyaml-dev postfix
 
     sudo pip install pygments