fix(definitions): remove RenderContext interface
fix(definitions): remove RenderContext interface

not needed for typescript builds after all, see:
https://github.com/opensheetmusicdisplay/opensheetmusicdisplay/issues/448#issuecomment-436941608

opensheetmusicdisplay/opensheetmusicdisplay,opensheetmusicdisplay/opensheetmusicdisplay,opensheetmusicdisplay/opensheetmusicdisplay