std: time: Avoid to use "was created" in elapsed() description

".. since this instant was created" is inaccurate and misleading,
consider the following case:

	let i1 = Instant::now(); // i1 is created at T1
	let i2 = i1 + Duration::from_nanos(0); // i2 is "created" at T2
	i2.elapsed(); // at T3

Per the current description, `elapsed()` at T3 should return T3 - T2?

Therefore removes the "was created" in the description of
{Instant,SystemTime}::elapsed(). And since these types represent times,
it's OK to use prepostions with them, e.g. "since this instant".

0 files changed, 0 insertions, 0 deletions