tests/basics/builtin_str_hex.py: Remove corresponding .exp file.

As of CPython 3.7 `bytes.fromhex()` skips all ASCII whitespace.  And as of
CPython 3.8 `bytes.hex()` supports the optional separator argument.  So
this test no longer needs a .exp file.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

tests/basics/builtin_str_hex.py

@@ -35,5 +35,5 @@
 ):
     try:
         print(bytes.fromhex(x))
-    except ValueError as e:
-        print("ValueError:", e)
+    except ValueError:
+        print("ValueError", x)