Cleanup: Clang-Tidy readability-redundant-declaration fix

No functional changes.

.clang-tidy

@@ -14,7 +14,6 @@ Checks:  >
 
   -readability-inconsistent-declaration-parameter-name,
   -readability-redundant-member-init,
-  -readability-redundant-declaration,
   -readability-qualified-auto,
   -readability-use-anyofallof,
 

source/blender/io/collada/DocumentExporter.cpp

@@ -106,8 +106,6 @@ extern "C" char build_hash[];
 #include "collada_internal.h"
 #include "collada_utils.h"
 
-extern bool bc_has_object_type(LinkNode *export_set, short obtype);
-
 // can probably go after refactor is complete
 #include "InstanceWriter.h"
 #include "TransformWriter.h"