Unreviewed, rolling out r220144.

Unreviewed, rolling out r220144.
https://bugs.webkit.org/show_bug.cgi?id=175276

"It did not actually speed things up in the way I expected"
(Requested by saamyjoon on #webkit).

Reverted changeset:

"On memory-constrained iOS devices, reduce the rate at which
the JS heap grows before a GC to try to keep more memory
available for the system"
https://bugs.webkit.org/show_bug.cgi?id=175041
http://trac.webkit.org/changeset/220144

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@220346 268f45cc-cd09-0410-ab3c-d52691b4dbfc