attr_file: remove invalid TODO comment

In our attributes pattern parsing code, we have a comment that
states we might have to convert '\' characters to '/' to have
proper POSIX paths. But in fact, '\' characters are valid inside
the string and act as escape mechanism for various characters,
which is why we never want to convert those to POSIX directory
separators. Furthermore, gitignore patterns are specified to only
treat '/' as directory separators.

Remove the comment to avoid future confusion.

src/attr_file.c

@@ -743,7 +743,6 @@ int git_attr_fnmatch__parse(
 	} else {
 		/* strip '\' that might have been used for internal whitespace */
 		spec->length = unescape_spaces(spec->pattern);
-		/* TODO: convert remaining '\' into '/' for POSIX ??? */
 	}
 
 	return 0;