Removing it seems to be a clear win on mobile: producing symbol data makes cold
parsing 20-30% slower, and having symbol data doesn't make warm parsing any
faster.

Notes:
- V8 used to produce symbol data, but because of a bug, it was never used until
recently. (See fix https://codereview.chromium.org/172753002 which takes the
symbol data into use again.)
- On desktop, warm parsing is faster if we have symbol data, and producing it
during cold parsing doesn't make parsing substantially slower. However, this
doesn't seem to be the case on mobile.
- The preparse data (cached data) will now contain only the positions of the
lazy functions.

BUG=
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/261273003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@21146 ce2b1a6d-e550-0410-aec6-3dcde31c8c00