[issue:307] newtx/newpx error with \pdfglyphtounicode

[Hironobu Yamashita]

Hi Michael,

After updating to newtxmath.sty version 1.60 (2019-09-27),
an error
> ! Undefined control sequence. for \pdfglyphtounicode.
occurs when we use \usepackage{newtxmath} with
lualatex, platex, uplatex.
These engines do not support \pdfglyphtounicode, so
I think the final code of newtxmath.sty should be inside

\ifx\pdfglyphtounicode\@undefined \else ... \fi

Similar issue for newpxmath.sty.
Could you support those engines again?

Thanks,
Hironobu Yamashita