Move profiler callback interfaces from v8.h to v8-profiler.h

OutputStream and ActivityControl are used only by heap profiler so I moved their definition in v8-profiler.h to not clutter v8.h

Drive-by: removed OutputStream::GetOutputEncoding which is unused.

BUG=None
LOG=Y
R=alph@chromium.org, svenpanne@chromium.org

Review URL: https://codereview.chromium.org/196383015

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19955 ce2b1a6d-e550-0410-aec6-3dcde31c8c00