Compositor: Limit C linkage of cryptomatte functions

Most of the functions in the compositor cryptomatte file are declared
with extern "C" linkage, which can cause symbol conflict even when
functions exist in separate namespaces. This is not actually necessary,
as the declaration of the few functions that require C linkage are
already declared as such in the header file, so this patch removes the
extern C scope from that file.

Differential Revision: https://developer.blender.org/D15656

Reviewed By: Clement Foucault

source/blender/nodes/composite/nodes/node_composite_cryptomatte.cc

@@ -107,7 +107,6 @@ static blender::bke::cryptomatte::CryptomatteSessionPtr cryptomatte_init_from_no
   return session;
 }
 
-extern "C" {
 static CryptomatteEntry *cryptomatte_find(const NodeCryptomatte &n, float encoded_hash)
 {
   LISTBASE_FOREACH (CryptomatteEntry *, entry, &n.entries) {
@@ -428,4 +427,3 @@ void register_node_type_cmp_cryptomatte_legacy()
 }
 
 /** \} */
-}