Rollup merge of #144894 - jieyouxu:chop-thread-cnt, r=ChrisDenton

Delete `tests/ui/threads-sendsync/tcp-stress.rs`

This stress test was originally introduced in 65cca4b to detect a UAF in `libuv` (see #12823), but we no longer use `libuv`, so remove this test as it no longer serves its original purpose, and is causing flaky timeout failures.

Closes #144878 (by removing the test).

r? libs

Author: samueltardieu