benchmark: use consistent coding style in assert/*

Files in benchmark/assert/* were sometimes using trailing commas for
multi-line objects and sometimes not, mixing the approaches in the same
file sometimes. Standardize these files to always use trailing commas in
multi-line objects.

Additionally, remove some unnecessary line-wrapping (so that there are
fewer multi-line objects).

PR-URL: https://github.com/nodejs/node/pull/25865


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>