Fix a compilation error in the debug build (#6689)

Fix debug builds

Signed-off-by: Filipe Laíns <lains@riseup.net>
Co-authored-by: SoftFever <softfeverever@gmail.com>

src/libslic3r/Model.cpp

@@ -2785,7 +2785,6 @@ std::vector<size_t> ModelVolume::get_extruders_from_multi_material_painting() co
      if (!this->is_mm_painted())
          return {};
 
-     assert(static_cast<size_t>(EnforcerBlockerType::Extruder1) - 1 == 0);
      const TriangleSelector::TriangleSplittingData &data = this->mmu_segmentation_facets.get_data();
 
      std::vector<size_t> extruders;