Update the benchmarks with modern tcmalloc

Use the tip or latest release from https://github.com/google/tcmalloc, not the old gperftools fork. It isn't really fair to label that fork "tcmalloc" anymore.

Locate the benchmark configuration and references to the old gperftools fork, then compare them with the tip or latest release from the linked google/tcmalloc repository. Done means the benchmarks use modern tcmalloc rather than labeling the old fork as tcmalloc; the issue names no specific files or tests.

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