Fix build with libmatroska 1.6.x

The MATROSKA_VERSION define is gone as it was an ancient compilation flag to support writing Matroska v1 files.

Since the EDocTypeReadVersion is 2, using 2 as the Matroska version of the file seems the correct value to use.

Fixes the issue mentioned here Matroska-Org/libmatroska#41 (comment)

src/record/sdk/record.cpp

@@ -543,7 +543,7 @@ k4a_result_t k4a_record_write_header(const k4a_record_t recording_handle)
             EbmlHead file_head;
 
             GetChild<EDocType>(file_head).SetValue("matroska");
-            GetChild<EDocTypeVersion>(file_head).SetValue(MATROSKA_VERSION);
+            GetChild<EDocTypeVersion>(file_head).SetValue(2);
             GetChild<EDocTypeReadVersion>(file_head).SetValue(2);
 
             file_head.Render(*context->ebml_file, true);