makelsr.py: don't delete the output directory

makelsr.py: don't delete the output directory

If the output directory is not a directory, don't just delete it. Abort and let the user decide how to address it.

I am pretty confident that these changes are good, but I would be grateful if someone familiar with this script would try running it because I can not test the full script myself.  (I have set up my build environment without write access to the source, so updating source files fails.  Yes, I have the expertise to change the approach, but I lack the interest.)