tests: Make bytes/str.count() tests skippable.

tests/basics/bytes_count.py

+try:
+    bytes.count
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
 print(b"".count(b""))
 print(b"".count(b"a"))
 print(b"a".count(b""))

tests/basics/string_count.py

+try:
+    str.count
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
 print("".count(""))
 print("".count("a"))
 print("a".count(""))

tests/misc/features.py

+try:
+    str.count
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
 # mad.py
 # Alf Clement 27-Mar-2014
 #