Ubuntu from source: consolidate apt deps

Include git in list of generic tools and remove a step from
dependency installation instructions.

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

Author: scpeters

ionic/install_ubuntu_src.md

@@ -24,7 +24,7 @@ cases where the default option cannot be easily changed.
 Install tools needed by this tutorial:
 
 ```bash
-sudo apt install python3-pip python3-venv lsb-release gnupg curl
+sudo apt install python3-pip python3-venv lsb-release gnupg curl git
 ```
 
 ## vcstool and colcon from pip
@@ -52,15 +52,6 @@ sudo apt-get update
 sudo apt-get install python3-vcstool python3-colcon-common-extensions
 ```
 
-## Git
-
-Gazebo libraries use `git` for version control, so it must be available
-in the system for `vcstool` to work properly.
-
-```bash
-sudo apt-get install git
-```
-
 ## Getting the sources
 
 The instructions below use some UNIX commands to manage directories but the