CDRIVER-4674 Remove unnecessary code from bson-clock.c

[joshbsiegel]

Summary

This PR will remove an elif block from bson_get_monotonic_time that checks if the driver is running on macOS as it serves no purpose anymore.

Background

https://jira.mongodb.org/browse/CDRIVER-4565 fixed an assertion failure that occasionally occurred on macOS 10.14. This involved using clock_gettime_nsec_np and CLOCK_UPTIME_RAW to get the monotonic time on macOS machines. However, because clock_gettime_nsec_np and CLOCK_UPTIME_RAW were introduced in macOS 10.12 and clock_gettime and CLOCK_MONOTONIC were introduced in OS X 10.11 (one of these must not be defined to hit the elif block in question), this function won't compile on OS X 10.10 or earlier.
As of now, all supported versions of macOS have clock_gettime and CLOCK_MONOTONIC, so this elif statement is no longer necessary. This PR will also ensure that the driver will compile on older versions of OS X, even if they are unable to use bson_get_monotonic_time sucessfully.

What's New

• Removed unnecessary code from bson_get_monotonic_time
• Removed unnecessary headers from bson-clock.c

[jmikola]

Is this include still needed? It dates back to mongodb/libbson@c6e981e, although it's not clear if it was specific to the use of mach_ functions since that commit also included it for the defined(HAVE_CLOCK_GETTIME) case.

[joshbsiegel]

Thanks for the catch. Based upon what I can see in time.h and backed up by this patch, I think we are good to remove all of the macOS includes.

[jmikola]

This entire #ifdef can be removed if it no longer has a body.

[joshbsiegel]

I thought I already did this and I have no idea why that commit wasn't showing before. I just made a new commit ("remove empty line") and now the "remove #ifdef" commit is showing 😕

[jmikola]

@kevinAlbs should probably still sign off on this.

[kevinAlbs]

even if they are unable to use bson_get_monotonic_time sucessfully.

I expect bson_get_monotonic_time will continue to "succeed" and fall back to the else case of using bson_gettimeofday, and show the "Monotonic clock is not yet supported on your platform" warning on compile.
I think that is OK. Support of macOS 10.14 and 10.15 was decidedly dropped in 1.24.0 as part of CDRIVER-4580.