COMP: Remove deprecated uses of vxl for LEGACY ITK

When ITK specifies removing support for LEGACY code
uses, then VXL should also remove support.

This patch sets "VXL_USE_HISTORICAL_IMPLICIT_CONVERSIONS=OFF"
when ITK_LEGACY_REMOVE or ITK_LEGACY_FUTURE_REMOVE is requested.

Modules/ThirdParty/VNL/CMakeLists.txt

@@ -23,6 +23,11 @@ else()
 
   # ITKv5 no longer supports legacy method signatures for VNL
   set(VNL_CONFIG_LEGACY_METHODS     OFF CACHE BOOL "Whether backward-compatibility methods are provided by vnl." FORCE )
+  if(ITK_LEGACY_REMOVE OR ITK_FUTURE_LEGACY_REMOVE)
+    set(VXL_USE_HISTORICAL_IMPLICIT_CONVERSIONS OFF CACHE BOOL "Allow default deprecated implicit conversions." FORCE )
+  else()
+    set(VXL_USE_HISTORICAL_IMPLICIT_CONVERSIONS ON  CACHE BOOL "Allow default deprecated implicit conversions." FORCE )
+  endif()
   set(VXL_BUILD_CORE_NUMERICS       ON  CACHE BOOL "VXL configuration for ITK" FORCE )
   set(VXL_BUILD_CORE_NUMERICS_ONLY  ON  CACHE BOOL "VXL configuration for ITK" FORCE ) #This hides other VXL core options from CMake
   set(VXL_NO_EXPORT                 ON  CACHE BOOL "VXL configuration for ITK" FORCE )