Revert "Add HEAP_EXPORT to ThreadHeap::outOfLineAllocate to fix linker errors on GCC/component build"

This reverts commit 325f4fd338d6ef04ce44f67edb72266c3af5807c.

This build fix for GCC is a build breakage on Windows, see a
previous attempt at the same fix at:

https://codereview.chromium.org/123813003/

TBR=vegorov@chromium.org

Review URL: https://codereview.chromium.org/127023002

git-svn-id: svn://svn.chromium.org/blink/trunk@164633 bbb929c8-8fbe-4397-9dbb-9b2b20218538