gas/NEWS: Remove mention of AArch64 B16B16 extension

This aligns the 2.42 NEWS with the update backported to the 2.42 release
branch.
diff --git a/gas/NEWS b/gas/NEWS
index 5d2a364..07e834e 100644
--- a/gas/NEWS
+++ b/gas/NEWS
@@ -16,9 +16,6 @@
 
 * Add support for AMD znver5 processor.
 
-* Add support for the AArch64 BFloat16 to BFloat16 arithmetic for SVE2
-  (B16B16).
-
 * Add support for the AArch64 Reliability, Availability and Serviceability
   extension v2 (RASv2).