[libc] Migrate some test/src/time tests to ErrnoCheckingTest. (#157960)

Use ErrnoCheckingTest harness to clear out / validate errno value
before/after the test respectively. Clean up explicit libc_errno.h
inclusions which is unnecessary, since no test modifies errno directly.

GitOrigin-RevId: b8e1cc5c72d1e4243a189b2516517bcd5de7ea18
8 files changed