Revert "MINOR: chunks: Make sure trash_size is only set once."

Revert "MINOR: chunks: Make sure trash_size is only set once."

This reverts commit 1c3b83242da96f1d94ef3df34c399c1b984668b6.

It was made only to silence the thread sanitizer but ends up creating a
bug. Indeed, if "tune.bufsize" is in the global section, the trash_size
value is not updated anymore and the trash becomes smaller than a buffer!

Let's stop trying to fix the thread sanitizer reports, they are invalid,
and trying to fix them actually introduces bugs where there were none.

See GH issue #117 for more context. No backport is needed.