Revert of Treat bad values passed to --images as a fatal error (patchset #17 id:32000...

Revert of Treat bad values passed to --images as a fatal error (patchset #17 id:320001 of https://codereview.chromium.org/1611323004/ )

Reason for revert:
Speculative to fix windows bots

Original issue's description:
> Treat bad values passed to --images as a fatal error
>
> If an option is passed to --images that is either a non-existent path or
> a folder with no images matching the supported types, assume this is
> an error and exit, so they can supply a valid path instead.
>
> Share code between DM and nanobench in SkCommonFlags.
>
> nanobench now behaves more like DM - it will check a directory for
> images that match the supported extensions.
>
> Only consider image paths ending in RAW suffixes as images if
> SK_CODE_DECODES_RAW is defined. This prevents us from seeing failure
> to decode errors on platforms that cannot decode it.
>
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1611323004
>
> Committed: https://skia.googlesource.com/skia/+/7579786f3bd5a8fda84a1abc45b16213c3371f93

TBR=mtklein@google.com,borenet@google.com,msarett@google.com

NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
# Not skipping CQ checks because original CL landed more than 1 days ago.

Review URL: https://codereview.chromium.org/1653543002