Remove unused fmudesign test data

Author: larsevj

tests/fmudesign/data/README.md

@@ -1,4 +1,5 @@
-Testdata for tornadoplots from one by one sensitivities (design matrix)
-distributions: contains design matrix on fmu standard format in excel and .csv format
-results: contains in place volumes exported from RMS in fmu standard csv format
-config: contains yaml config files for add_webviz_tornado_onebyone.py
+Test data for FMU-design.
+
+`config` contains legacy workbook inputs exercised by the CLI smoke tests and
+their external background and seed data. Focused tests generate smaller
+workbooks at runtime instead of relying on additional binary fixtures.