refactor: remove is-plain-obj

[Jayllyz]

Changes

Removed is-plain-obj in favor of a oneline function.

Context

As part of the ongoing ecosystem cleanup, we are migrating various projects to use lighter/faster package or alternatives.

https://github.com/TheDevMinerTV/package-size-calculator

How I've tested my work

npm run test 4982 tests passed

[sindresorhus]

Not sure I see the point of this. This will have very little impact on the cleanup effort. The real problems in the ecosystem is that certain packages support too low Node.js versions and include polyfills for everything. This also feels like a slippery slope to inline even more, which means code gets duplicated, and potential bug fixes or improvements don't get included.

The proper fix would be to convince TC39 to add a method like this to JS: https://es.discourse.group

[ehmicky]

100% agree with @sindresorhus. 👍