Revert of SkPDF: Optionally output PDF/A-2b archive format.

Revert of SkPDF: Optionally output PDF/A-2b  archive format. (patchset #5 id:80001 of https://codereview.chromium.org/1394263003/ )

Reason for revert:
SkMD5 is not really part of the Skia library. This is breaking the roll by using it, since Chromium doesn't build it.

Original issue's description:
> SkPDF: Optionally output PDF/A-2b  archive format.
> 
> Note: this format does not yet pass validation tests.
> 
> Add skia_pdf_generate_pdfa GYP flag.  Default to off for now.
> PDF/A files are not reproducable, so they make correctness
> testing harder.
> 
> Turn the Metadata struct into te SkPDFMetadata struct.  This
> splits out a lot of functionality around both kinds of metadata.
> 
> When PDF/A is used, add an ID entry to the trailer.
> 
> Add SkPDFObjNumMap::addObjectRecursively.
> 
> Test with
> 
>     GYP_DEFINES=skia_pdf_generate_pdfa=1 bin/sync-and-gyp
>     ninja -C out/Release dm
>     out/Release/dm --config pdf --src skp gm -w /tmp/dm
> 
> With skia_pdf_generate_pdfa=0, all PDFs generated from GMs and
> SKPs are identical.  With skia_pdf_generate_pdfa=1, all PDFs
> generated from GMs and SKPs render identically in Pdfium.
> 
> BUG=skia:3110
> 
> Committed: https://skia.googlesource.com/skia/+/939c0fe51f157104758bcb268643c8b6d317a530

TBR=tomhudson@google.com,halcanary@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:3110
Committed: https://skia.googlesource.com/skia/+/21f99b7733c5d468deee9f8dadd59e77ed33d5ca

[bungeman-skia, 2015-10-09 20:45:37]

Created Revert of SkPDF: Optionally output PDF/A-2b  archive format.

[commit-bot: I haz the power, 2015-10-09 20:45:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1398193002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1398193002/1

[commit-bot: I haz the power, 2015-10-09 20:45:56]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/21f99b7733c5d468deee9f8dadd59e77ed33d5ca