Removing gcc-multilib from ubuntu host dependency

gcc-multilib is conflicting with gcc-aarch64-linux-gnu and g++-aarch64-linux-gnu packages. 
Which are required: Xilinx#59 (comment)

sphinx/source/docs/install.md

@@ -183,7 +183,7 @@ Cross-compilation of ROS 2 workspaces allows to build both CPU binaries as well
 sudo apt-get -y install curl build-essential libssl-dev git wget \
                           ocl-icd-* opencl-headers python3-vcstool \
                           python3-colcon-common-extensions python3-colcon-mixin \
-                          kpartx u-boot-tools pv gcc-multilib gcc-aarch64-linux-gnu g++-aarch64-linux-gnu
+                          kpartx u-boot-tools pv gcc-aarch64-linux-gnu g++-aarch64-linux-gnu
 
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 # 2. create a new ROS 2 workspace with examples and