refactor: remove deprecated NzBackTopModule (#9530)

Author: Laffery

.github/CODEOWNERS

@@ -1,7 +1,6 @@
 # The components owners
 components/affix/**                       @cipchk
 components/anchor/**                      @cipchk
-components/back-top/**                    @cipchk
 components/list/**                        @cipchk
 components/upload/**                      @cipchk
 components/auto-complete/**               @hsuanxyz

.github/nz-boot.yml

@@ -62,7 +62,6 @@ issue:
     components:
       Affix: cipchk
       Anchor: cipchk
-      BackTop: cipchk
       List: cipchk
       Upload: cipchk
       AutoComplete: hsuanxyz