There's no RST file that uses ".. math" and thus
the pngmath Sphinx extension is not used and can get
removed.
Change-Id: I3ea4b529025c8ac3c4092f3720124647861e6668
os.popen() is deprecated since python 2.6.
Resolved with use of subprocess module.
Change-Id: I343d34f43ab7a1472040c3c2aca920c0e4fa1aa8
Closes-Bug: #1529836