Minor fixes for XML persistence generation.

The Android checkstyle configuration requires exactly the string
"CHECKSTYLE: OFF Generated Code" in its SuppressionCommentFilter.

JLS 4.12.4 says try-with-resources declaration is implicitly final,
hence drop the redundant final modifier in generated code.

Test: manual
Change-Id: Idbb703d950601c32aececfc45e480698657ef764