fix previous commit, for #215 remove date fields from librarymapping sheet

Fixes the "re_run.sh test" build script functionality.
- broken in 06b61b985e7f636a2a8192ab511ad2cbae93ce56 ; wherein these fields were removed from the library importer.
- removes the date fields from the "LibraryMapping" sheet of the sampledata/libraries.xls file.