RFR: 8135284: Remove Method::_method_size field

[Yumin Qi]

Please review the small changes for

bug: https://bugs.openjdk.java.net/browse/JDK-8135284
webrev: http://cr.openjdk.java.net/~minqi/8135284/webrev00/

Summary: After JDK-8135085 integration, Method increased 4 bytes for 
32-bit platforms(no effect for 64 bit). This change removed _method_size 
from Method which saved 2 bytes for Method. Deleted method_size related 
code in SA. The Method size is a constant in Method Type, if it is 
native method then _*TWO*_ words added which is consistent with hotspot 
code. btyecodeOffset in Method.java is no longer useful, the offset is 
now in ConstMethod so removed too.

Tests: JPRT, Runtime Quick test list, run SA on 
sun.jvm.hotspot.tools.ClassLoaderStats (instrumented Method output to 
get size).

Thanks
Yumin