In Node.js 14.14.0 the `fs.rmSync` function was added that removes files
and directories. The `recursive` option is used to remove directories
and their contents, making it a drop-in replacement for the `rimraf`
dependency we use.
Given that PDF.js now requires Node.js 18+ we can be sure that this
option is available, so we can safely remove `rimraf` and reduce the
number of project dependencies in the test folder.
This commit also gets rid of the indirection via the `removeDirSync`
test helper function by simply calling `fs.rmSync` directly.
Co-authored-by: Wojciech Maj <kontakt@wojtekmaj.pl>
