Remove ParameterType_Empty

Summary

ParameterType_Empty was deprecated in 6.6.0 (in !15 (merged)). This MR removes it for 7.0.0.

Rationale

Closes #1770 (closed).

Copyright

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

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Check before merging:

• All discussions are resolved
• At least 2 votes from core developers, no vote.
• The feature branch is (reasonably) up-to-date with the base branch
• Dashboard is green
• Copyright owner has signed the ORFEO ToolBox Contributor License Agreement

changed title from REFAC: remove ParameterType_Empty to Remove ParameterType_Empty

changed the description

dashboard looks sort of green, needs votes

mentioned in commit c3fa194e

merged