Lingering comment documenting `ECMULT_WINDOW_SIZE` large values' costs

[hebasto]

The following comment:

secp256k1/src/ecmult_impl.h

Lines 33 to 41 in 7a2fff8

	/** Larger values for ECMULT_WINDOW_SIZE result in possibly better
	* performance at the cost of an exponentially larger precomputed
	* table. The exact table size is
	* (1 << (WINDOW_G - 2)) * sizeof(secp256k1_ge_storage) bytes,
	* where sizeof(secp256k1_ge_storage) is typically 64 bytes but can
	* be larger due to platform-specific padding and alignment.
	* Two tables of this size are used (due to the endomorphism
	* optimization).
	*/

appears quite confusing to me, as it refers to WINDOW_G, while residing in the code that sets WINDOW_A.

This comment became lingering and out of context since commit 6815761.

Removing it seems reasonable, as its content is already covered by the --with-ecmult-window configuration option help string. However, this would overlook its original purpose to document the ECMULT_WINDOW_SIZE definition when our build system is not used.