Omit unnecessary \ before paren in C docstrings

Omit unnecessary \ before paren in C docstrings

Although \( is needed in docstrings in Elisp code, it is not needed in
docstrings in C code, since C function definitiions do not start with
a parenthesis.  The backslashes made the docstrings a bit harder to
read and to format in columns.  Also, some C docstrings had ( in
column 1 and this did not appear to be causing any problems.  So,
simplify C docstrings by replacing \( with ( and \) with ).