Revert "c.zig: Add definition for pthread_key_t"

This reverts commit aa3964477f662ea5487aa4a1e4595d174e49a89d.

This declaration is already provided by operating-system-specific files.
This is not the correct solution to the problem.

See #14013
Reopens #13950
775b0c1347Andrew Kelley committed on 12/20/2022, 9:37:05 PMparente1345fd
1 file changedLine totals unavailable