Remove annotations for synthetic methods on PrintWriter.

The process used to generate the ojluni.jaif snippet for PrintWriter
was including annotations for two synthetic brige methods which the
compiler generates for each overload of various append() (because the
PrintWriter methods narrow the return types of the Writer methods
which narrow the return types of the Appendable methods). Since the
bridge methods don't exist in source, they should not be annotated,
and the process to insert the annotations back into the source was
issuing warnings and ignoring them.

This change removes the warnings and does not change the output.

Test: make metalava-api-stubs-docs
Change-Id: I443bdc9e445974de7752f83daeaadd6cb8f8faed