Cleanup more

Cleanup more

I am removing few other things from the seh-unwind.cpp. First, the code that verified the
stack unwindibility actually couldn't work since in most cases, it would reach a managed
frame and then get screwed. It happened to few people in the recent past and they
were mislead into thinking that it is a problem of the coreclr unwinder.
There is no reasonable way to find out whether a frame is managed or native inside PAL,
that's why I am removign that stuff.
Also, there was now unused vectored exception handling stuff that I am also removing.
Another change is in the pal.h / pal.cpp where the type of the argv parameter was
const char **argv, which prevented passing in char** (the compiler was ok with it in C,
but failed in C++). I have changed it to const char * const *argv, which allows
passing in the char** as well.