add docs compat

Author: vtjnash

doc/src/base/multi-threading.md

@@ -26,6 +26,7 @@ Base.@atomic
 Base.@atomicswap
 Base.@atomicreplace
 Base.@atomiconce
+Base.AtomicMemory
 ```
 
 There are also optional memory ordering parameters for the `unsafe` set of functions, that

doc/src/devdocs/builtins.md

@@ -12,7 +12,6 @@ Core.memoryrefoffset
 Core.memoryrefget
 Core.memoryrefset!
 Core.memoryref_isassigned
-Core.memoryrefsetonce!
 Core.memoryrefswap!
 Core.memoryrefmodify!
 Core.memoryrefreplace!