Remove stdio lock methods

[KamilaBorowska]

Fixes #805.

[dignifiedquire]

sad, but the right thing to do until we have a correct implementation. Thank you

[KamilaBorowska]

I personally don't think it's possible to have a correct implementation that inter-ops with standard library's locks because of standard library's choice to have a reentrant mutex.

It may be possible to skip the standard library, and directly call C API directly. This should be sound on POSIX platforms (I'm not sure about non-POSIX platforms). Sure, it may lead to garbage reads and writes (https://pubs.opengroup.org/onlinepubs/9699919799/functions/read.html says that "The behavior of multiple concurrent reads on the same pipe, FIFO, or terminal device is unspecified") when sync I/O operations and async I/O operations are combined, but strictly speaking that's not unsafe.