hotspot/graal: simplify CTW logic. now, the following configurations are supported: (1) CTW with Graal, graal compiled by itself with bootstrap (--vm graal -XX:+BootstrapGraal -XX:-TieredCompilation -XX:+CompileTheWorld) (2) CTW with Graal, graal compiled by C1/itself aka. tiered with bootstrap (--vm graal -XX:+BootstrapGraal -XX:+TieredCompilation +XX:+CompileTheWorld) (3) CTW with Graal, graal compiled by itself without bootstrap (--vm graal -XX:-BootstrapGraal -XX:-TieredCompilation -XX:+CompileTheWorld) (4) CTW with Graal, graal compiled by C1/itself aka. tiered without bootstrap (--vm graal -XX:-BootstrapGraal -XX:+TieredCompilation -XX:+CompileTheWorld) (5) CTW with Graal, graal compiled by C1/C2 aka. hosted (--vm server -XX:+CompileTheWorld)