Revert "Add StaleWhileRevalidateExperiment histograms."

This reverts commit 51d6bcfd10cb847da284a7aa1202f92ea37b74ca. It looks like it
might have introduced a new static initializer, though I can't tell where.
See https://build.chromium.org/p/chromium/builders/Linux/builds/68841/steps/sizes/logs/stdio
(there is a new SI detected in
stale_while_revalidate_experiment_domains.cc _GLOBAL__sub_I_stale_while_revalidate_experiment_domains.cc+0xb)

BUG=348877
TBR=ricea@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1466313005

Cr-Commit-Position: refs/heads/master@{#361592}
14 files changed