Remove support for signed 32-bit time_t
Now there are couple of requirements:
- All user space must be compiled with a 64-bit time_t, which are supported in the musl-1.2 and glibc-2.32 releases, along with installed kernel headers from linux-5.6 or higher.
See for details: https://lkml.org/lkml/2020/1/29/355?anz=web