Fix Superbuild default OTB_DATA_ROOT

Summary

Change the default OTB_DATA_ROOT to ${OTB-SuperBuild_SOURCE_DIR}/../Data in Superbuild.

Rationale

There is a OTB_DATA_ROOT cmake variable in the SuperBuild project. Currently, this variable is initialized with :

find_path(OTB_DATA_ROOT README-OTB-Data
  PATHS
  $ENV{OTB_DATA_ROOT}
  ${OTB-SuperBuild_SOURCE_DIR}/../../OTB-Data)

But the default location for the data folder in OTB is now OTB_SRC/Data (since the migration to git lfs), so we should modify the default accordingly, as it is done in the OTB project.

This MR also removes the $ENV{OTB_DATA_ROOT} from PATHS/HINTS option of find_path in otb and Superbuild. The right way to set a custom data root is to add a cmake option -DOTB_DATA_ROOT when calling cmake.

Additional notes

This MR will be tested as superbuild branch on the dashboard. It is probably the cause of most of the failing tests on windows platforms.

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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