Stop auto-adjusting the number of chunks when the chunk size is capped

This is counter-intuitive and could lead to extreme values, for
example:

	default: chunk_exponent = 20, dsk_reserve_chunks 4

	adjusted to: 12, 4 << 8 = 1024

now user sets chunk_exponent = 21

	adjusted to: 12, 1024 << 9 = 524288

Could have caused #5, related to #10

src/fellow_tune.c

@@ -94,8 +94,6 @@ stvfe_tune_check(struct stvfe_tune *tune)
 		    (size_t)1 << l, l,
 		    (size_t)1 << CHUNK_SHIFT,
 		    (size_t)1 << MIN_FELLOW_BITS, (unsigned)MIN_FELLOW_BITS);
-		tune->mem_reserve_chunks <<= (tune->chunk_exponent - l);
-		tune->dsk_reserve_chunks <<= (tune->chunk_exponent - l);
 		tune->chunk_exponent = l;
 	}