Revert "compiler/natives/src/reflect: Return true in IsNil for implicitly converted nil interface."
Revert "compiler/natives/src/reflect: Return true in IsNil for implicitly converted nil interface."

This reverts commit 1fb1aaaca99f647eaf7ca2ce6b3bc1f8aab27ef8.

The change in that commit was not a complete and correct solution.
Instead of resolving the underlying problem, it masked a symptom,
allowing the TestCallConvert test to pass.

A better fix will follow next.

gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs