readme: Remove duplicate 'is thrown'

Author: nirs

README.md

@@ -75,9 +75,9 @@ Notes:
    printf-style substitution is not supported. Perform any
    substitution using Python's % operator or .format() capabilities
    first.
- * A ValueError is thrown is thrown if sd_journald_sendv() results in
-   an error. This might happen if there are no arguments or one of them
-   is invalid.
+ * A ValueError is thrown if sd_journald_sendv() results in an error.
+   This might happen if there are no arguments or one of them is
+   invalid.
 
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