Use SourcePath in more places

Now that SourcePath uses a SourceAccessor instead of an InputAccessor,
we can use it in function signatures instead of passing a
SourceAccessor and CanonPath separately.

src/libstore/legacy-ssh-store.hh

@@ -60,8 +60,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
 
     StorePath addToStore(
         std::string_view name,
-        SourceAccessor & accessor,
-        const CanonPath & srcPath,
+        const SourcePath & path,
         ContentAddressMethod method,
         HashAlgorithm hashAlgo,
         const StorePathSet & references,