[lldb] Remove memory region non-address change from release notes

This is now on 14.x as af19ae529271f9ae96927662d7d876489115fb26
so it is not new to 15.

Author: DavidSpickett

llvm/docs/ReleaseNotes.rst

@@ -145,12 +145,6 @@ Changes to the LLVM tools
 Changes to LLDB
 ---------------------------------
 
-* The ``memory region`` command and ``GetMemoryRegionInfo`` API method now
-  ignore non-address bits in the address parameter. This also means that on
-  systems with non-address bits the last (usually unmapped) memory region
-  will not extend to 0xF...F. Instead it will end at the end of the mappable
-  range that the virtual address size allows.
-
 Changes to Sanitizers
 ---------------------