remove acting_version from encoder

Author: suremarc

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/rust/RustGenerator.java

@@ -1357,7 +1357,6 @@ private static void generateCompositeEncoder(
  indent(out, 1, "pub struct %s<P> {\n", encoderName);
  indent(out, 2, "parent: Option<P>,\n");
  indent(out, 2, "offset: usize,\n");
- indent(out, 2, "acting_version: usize,\n");
  indent(out, 1, "}\n\n");
 
  appendImplWriterForComposite(out, 1, encoderName);