While skimming C1 code, I found a lot of useless/invalid/unimplemented code, they can be harmless removed.

- Unused IntInterval in type hierarchy
- Unused MethodDataConstant in type hierarchy
- Unused MethodDataType in type hierarchy
- Unused LIRGenerator::maybe_mask_boolean after JDK-XXX...
- Unused is_*_stub() **virtual methods** in CodeStub
- Unused start_block and bind_block_entry declarations in c1_LIRGenerator.hpp
- Residual do_ClassIDIntrinsic declarations in c1_LIRGenerator.hpp
- Meet/join are never implemented
- LIRTracePeephole does nothing, also its name is confusing
- Directly define inline functions in c1_ValueSet.hpp and remove c1_ValueSet.inline.hpp and c1_ValueSet.cpp files
- Duplicated Compilation::count_invocations() and Compilation::count_backedges()
- Remove c1_Defs.cpp
- Remove lir_backwardbranch_target