This saves ~50Mb for vyos-build image: 2.04Gb -> 1.99Gb
And ~19Mb for vyos image: 155Mb -> 136Mb
Docker stores all files created in each layer so
command
```
RUN wget -O /tmp/open-vmdk-master.zip https://github.com/.../master.zip && \
unzip -d /tmp/ /tmp/open-vmdk-master.zip && \
cd /tmp/open-vmdk-master/ && make && make install
```
will store open-vmdk-master.zip and /tmp/open-vmdk-master
in the image even though there is a cleanup command later:
```
RUN rm -rf /tmp/*
```
The cleanup command just makes these files invisible in last layer.
So temporary file must be removed in same RUN command
not to be stored in the image.
This commit adds such removals.
As we got rid of most of the old vyatta packages we can now also discontinue
vyos-world. It only served the purpose of keeping the package list during ISO
build small.
