bpo-29770: remove outdated PYO related info (GH-590)

diff --git a/Modules/main.c b/Modules/main.c
index 633e757..0951b3f 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -53,7 +53,7 @@
 Options and arguments (and corresponding environment variables):\n\
 -b     : issue warnings about str(bytes_instance), str(bytearray_instance)\n\
          and comparing bytes/bytearray with str. (-bb: issue errors)\n\
--B     : don't write .py[co] files on import; also PYTHONDONTWRITEBYTECODE=x\n\
+-B     : don't write .pyc files on import; also PYTHONDONTWRITEBYTECODE=x\n\
 -c cmd : program passed in as string (terminates option list)\n\
 -d     : debug output from parser; also PYTHONDEBUG=x\n\
 -E     : ignore PYTHON* environment variables (such as PYTHONPATH)\n\