configure: remove DIRS

configure: remove DIRS

DIRS is used to create the directory in which the LINKS symbolic links
reside, or to create directories for object files.  The former can
be done directly in the symlinking loop, while the latter is done
by Meson already, so DIRS is not necessary.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>