Revert "fix #15836 proc arg return type auto unexpectly match proc with concr…" (#21057)

Revert "fix #15836 proc arg return type auto unexpectly match proc with concr… (#21044)"

This reverts commit 0cd9bdcf9f.

tests/types/t15836.nim

@@ -1,11 +0,0 @@
-discard """
-  errormsg: "type mismatch: got <string> but expected 'int'"
-  line: 11
-""" 
-
-proc takesProc[T](x: T, f: proc(x: T): int) =
-    echo f(x) + 2
-
-takesProc(1, proc (a: int): int = 2) # ok, prints 4
-takesProc(1, proc (a: auto): auto = 2) # ok, prints 4
-takesProc(1, proc (a: auto): auto = "uh uh") # prints garbage