perfetto: remove redundant genrule in ipc target
perfetto: remove redundant genrule in ipc target

For IPC targets, we always generate an _cpp target in our generator and
add it to our BUILD file so there is no need to do it again in the build
rule.

Removing this fixes the buid in the internal tree.

Change-Id: Idbf314adc6937097eb970c126fbc937498eae31a
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto