gh-137562: Remove obsolete comment about calculating incremental threshold

[sergey-miryanov]

gc.c/SCAN_RATE_DIVISOR has obsolete comment about calculating incremental threshold based on count of survivors. It is obsolete since #117120

cpython/Python/gc.c

Lines 1345 to 1362 in 34d7351

	/* Making progress in the incremental collector
	* In order to eventually collect all cycles
	* the incremental collector must progress through the old
	* space faster than objects are added to the old space.
	*
	* Each young or incremental collection adds a number of
	* objects, S (for survivors) to the old space, and
	* incremental collectors scan I objects from the old space.
	* I > S must be true. We also want I > S * N to be where
	* N > 1. Higher values of N mean that the old space is
	* scanned more rapidly.
	* The default incremental threshold of 10 translates to
	* N == 1.4 (1 + 4/threshold)
	*/
	/* Divide by 10, so that the default incremental threshold of 10
	* scans objects at 1% of the heap size */
	#defineSCAN_RATE_DIVISOR 10

• Issue: Fix obsolete comments in gc.c #137562

[sergey-miryanov]

I believe this should skip news.

[sergey-miryanov]

@markshannon@nascheme Please take a look.

[sergey-miryanov]

@markshannon Could you also take a look at this one?