proto->cpp gen: remove unnecessary branch.
proto->cpp gen: remove unnecessary branch.

Repeated fields cannot be lazy. The add() code for
sub-messages and PODs is the same. The generated code is
hence identical. No need for two identical codegen paths.

Bug: 132880619
Change-Id: I0e78257d44438766dfb4fa2b1568e0fe6c126242
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto