remove time.h include from folly-config.h

Summary:
`folly-config.h` included `time.h` in order to test for the `CLOCK_REALTIME` macro, which was a proxy to test for the `clock_gettime` function. This was for Apple platforms, which ages ago did not all export `clock_gettime`. But current and recent Apple platforms should all export it.

Also cut `glibc-rt` and `liburing` deps from `folly:config`.

The rule owning this header should depend on nothing.

`autodeps` and `arc lint` breakage involving these deps originally reported by DenisYaroshevskiy in: https://fb.workplace.com/groups/560979627394613/posts/2913288488830370/.

#buildall

Reviewed By: spikeh

Differential Revision: D56805126

fbshipit-source-id: 7894de40c6de234ef05e8754ae6a733987a15477

Author: yfeldblum

folly/BUCK

@@ -223,16 +223,6 @@ cpp_library(
 cpp_library(
     name = "config",
     headers = ["folly-config.h"],
-    os_deps = [(
-        "linux",
-        select({
-            "DEFAULT": [],
-            "ovr_config//runtime:fbcode": ["fbsource//third-party/liburing:uring"],
-        }),
-    )],
-    exported_external_deps = [
-        ("glibc", None, "rt"),
-    ],
 )
 
 cpp_library(