remove UndefVarError deprecation from v0.5 (JuliaLang#40333)

Looks like this got lost in deprecation removal?

Author: vtjnash

base/errorshow.jl

@@ -163,16 +163,6 @@ function showerror(io::IO, ex::UndefVarError)
     Experimental.show_error_hints(io, ex)
 end
 
-Experimental.register_error_hint(UndefVarError) do io::IO, ex::UndefVarError
-    if ex.var in [:UTF16String, :UTF32String, :WString, :utf16, :utf32, :wstring, :RepString]
-        println(io)
-        print(io, """
-            `$(ex.var)` has been moved to the package LegacyStrings.jl:
-            Run Pkg.add("LegacyStrings") to install LegacyStrings on Julia v0.5-;
-            Then do `using LegacyStrings` to get `$(ex.var)`.""")
-    end
-end
-
 function showerror(io::IO, ex::InexactError)
     print(io, "InexactError: ", ex.func, '(')
     nameof(ex.T) === ex.func || print(io, ex.T, ", ")

test/errorshow.jl

@@ -796,5 +796,3 @@ if Sys.isapple() || (Sys.islinux() && Sys.ARCH === :x86_64)
         end
     end
 end  # Sys.isapple()
-
-@test contains(sprint(Base.showerror, UndefVarError(:UTF16String)), "LegacyStrings")