Code compiled during snapshot are overwhelmingly for functions
that are only used for bootstrapping. It makes no sense to
include them in the startup snapshot, which bloats up the snapshot size
and slows down deserialization.

Snapshot sizes for comparison, for ia32:
w/o --ignition:   484k
w/ --ignition:    537k
bytecode removed: 489k

R=rmcilroy@chromium.org,mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/1667693002

Cr-Commit-Position: refs/heads/master@{#33734}