Bug#1028097: mplcursors: remove Build-Depends: libopenblas0 (use libblas-dev instead)

[Drew Parsons]

Actually looking more closely at the source, mplcursors doesn't even use 
BLAS at all.

In that case just remove the libopenblas0 dependency altogether (both 
Build-Depends: and Depends: for the binary package).