Remove unused code from CharsetBenchmark.

This in preparation for removing UnsafeBytesequence.
Split into a separate change so that it's easier to
resurrect if required.

(Cherry picked from 71852e47df6b12fde7103bc559dd2d756eb8ddc4)

Bug: b/11411129
Change-Id: I24b8cd6a56a37d4efc23cfea0b59adc0f065f5a2
1 file changed