Remove GraphicsContext constructor that takes shouldUseContextColors

Remove GraphicsContext constructor that takes shouldUseContextColors
https://bugs.webkit.org/show_bug.cgi?id=136421

Reviewed by Dan Bernstein.

* WebCore.exp.in:
* platform/graphics/GraphicsContext.cpp:
(WebCore::GraphicsContext::GraphicsContext):
* platform/graphics/GraphicsContext.h:
(WebCore::GraphicsContextState::GraphicsContextState):
* platform/graphics/cg/GraphicsContextCG.cpp:
(WebCore::GraphicsContext::platformInit):
(WebCore::GraphicsContext::drawLinesForText):
As far as I can tell, the last user of this constructor died with WebNSStringDrawing.
Adjust all code to assume shouldUseContextColors=true.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@173152 268f45cc-cd09-0410-ab3c-d52691b4dbfc