Revert of MIPS: Fix mksnapshot on big-endian. (patchset #3 id:40001 of https://codereview.chromium.org/2172653002/ )

Reason for revert:
Blocks the roll:
https://codereview.chromium.org/2189443003/

Doesn't work with the last chromium gyp bot.

Original issue's description:
> MIPS: Fix mksnapshot on big-endian.
>
> Paritally revert standalone.gypi changes in a451bd1a and introduce a new separate variable for the mkpeephole.
>
> On big-endian MIPS, qemu is used to build the snapshot,
> because there's no simulator support for big-endian MIPS.
>
> BUG=
>
> Committed: https://crrev.com/928d2395c3fdf836cf9961cde96e6b274a6b1e20
> Cr-Commit-Position: refs/heads/master@{#38103}

TBR=oth@chromium.org,machenbach@google.com,akos.palfi@imgtec.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2182633010
Cr-Commit-Position: refs/heads/master@{#38108}