tests/cpydiff: Remove types_str_decodeerror now that it succeeds.

Commit 68c28174d0 implemented checking for
valid utf-8 data.

tests/cpydiff/types_str_decodeerror.py

@@ -1,11 +0,0 @@
-"""
-categories: Types,str
-description: UnicodeDecodeError not raised when expected
-cause: Unknown
-workaround: Unknown
-"""
-try:
-    print(repr(str(b"\xa1\x80", 'utf8')))
-    print('Should not get here')
-except UnicodeDecodeError:
-    print('UnicodeDecodeError')