build(node): don't throw on deprecation in unit tests

[gcf-owl-bot[bot]]

Fixes #1134 🦕

Removes the commit body and relative PR# from the commit message.

For example, for this commit: https://github.com/googleapis/synthtool/commit/9763f20e4b7bb1091082462b2f7970e965d0d414

post-processor-changes.txt would contain

build: enable npm for php/python builds

Source-Link: https://github.com/googleapis/synthtool/commit/9763f20e4b7bb1091082462b2f7970e965d0d414

instead of

build: enable npm for php/python builds (#1133)

* build: enable npm for php/python builds

* update comment
Source-Link: https://github.com/googleapis/synthtool/commit/9763f20e4b7bb1091082462b2f7970e965d0d414

Source-Link: https://github.com/googleapis/synthtool/commit/e934b93402284f834b510ebbf421864e881dce02 Post-Processor: gcr.io/repo-automation-bots/owlbot-nodejs:latest@sha256:805e2e389eafefa5ed484c30b83a7a875e6b1c7ee125d812e8b01ecc531c3fac