* tests/Makefile.am (lens_tests): explicitly remove target
* tests/Makefile.am (lens_tests): explicitly remove target

Debian's debhelper will, by default, run autoreconf, which leads to
problems as released tarballs contain copies of the various lens-*.sh
tests. autoreconf triggers an attempt to recreate the symbolic links to
those tests via 'ln -s', which fails because there are already ordinary
files for that in place.

To work aroun that, explicitly remove the 'lens-*.sh' scripts before
creating a symbolic link to them.

For background on Debian's rationale for running autoreconf, see
https://wiki.debian.org/Autoreconf

Fixes https://github.com/hercules-team/augeas/issues/511

mlichvar/augeas,kunkku/augeas,ptoscano/augeas,lutter/augeas,kunkku/augeas,mlichvar/augeas,ptoscano/augeas,lutter/augeas,mlichvar/augeas,ptoscano/augeas,hercules-team/augeas,kunkku/augeas,lutter/augeas,hercules-team/augeas