Revert "The blanket impl works with Infallible now"

Same reason as for the parent commit.

This reverts commit 0dd1825.

Author: mzabaluev

src/lib.rs

@@ -79,6 +79,8 @@ impl<T> UnwrapInfallible for Result<T, Infallible> {
 mod tests {
     use super::UnwrapInfallible;
 
+    // Hmm, Infallible is not Into<!> yet
+    #[cfg(not(feature = "blanket_impl"))]
     #[test]
     fn with_infallible() {
         use core::convert::TryFrom;