Correct the benchmarking dependencies of the runtime

[MOZGIII]

Details

After we merged #441 I noticed the cargo run -- --dev fails with an odd error:

Cannot create a runtime error=Other("runtime requires function imports which are not present on the host: 'env:ext_benchmarking_reset_read_write_count_version_1', 'env:ext_benchmarking_get_read_and_written_keys_version_1', 'env:ext_benchmarking_set_whitelist_version_1', 'env:ext_benchmarking_proof_size_version_1', 'env:ext_benchmarking_wipe_db_version_1', 'env:ext_benchmarking_read_write_count_version_1', 'env:ext_benchmarking_commit_db_version_1', 'env:ext_benchmarking_current_time_version_1', 'env:ext_benchmarking_add_to_whitelist_version_1'")

Investigating led me to this fix, which makes cargo run -- --dev work. Not sure why it is breaking without it. Might be some issue with caching of the build artifacts on my local system, idk.

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Still, regardless of the above, this PR actually removes one dependency when we're not in the benchmarking mode.