docs: removed repeated word

docs/howitworks.rst

@@ -57,7 +57,7 @@ writing the decompressed result to the write-end of the UNIX pipe.
 
 To allow recovery of ``stdin`` for reuse by the bootstrapped process for
 parent<->child communication, it is necessary for the first stage to avoid
-closing ``stdin`` or reading from it until until EOF. Therefore, the master
+closing ``stdin`` or reading from it until EOF. Therefore, the master
 sends the :py:mod:`zlib`-compressed payload prefixed with an integer size,
 allowing reading by the first stage of exactly the required bytes.