Step down as a WebAssembly backend maintainer. (#147404)

I plan to continue as a contributor and reviewer for the LLVM
WebAssembly backend, however I'm stepping down from the official
maintainer responsibilities.

Author: sunfishcode

llvm/Maintainers.md

@@ -298,9 +298,6 @@ marukawa@nec.com (email), [kaz7](https://github.com/kaz7) (GitHub)
 
 #### WebAssembly backend
 
-Dan Gohman \
-llvm@sunfishcode.online (email), [sunfishcode](https://github.com/sunfishcode) (GitHub)
-
 #### X86 backend
 
 Simon Pilgrim \
@@ -522,6 +519,7 @@ Michael Spencer (bigcheesegs@gmail.com), [Bigcheese](https://github.com/Bigchees
 Alexei Starovoitov (alexei.starovoitov@gmail.com, [4ast](https://github.com/4ast)) -- BPF backend \
 Evgeniy Stepanov ([eugenis](https://github.com/eugenis)) -- Sanitizers \
 Zheng Chen (czhengsz@cn.ibm.com, [chenzheng1030](https://github.com/chenzheng1030)) -- PowerPC backend
+Dan Gohman (llvm@sunfishcode.online, [sunfishcode](https://github.com/sunfishcode)) -- WebAssembly backend
 
 ### Former maintainers of removed components