Get rid of backtrace machinery

It is currently very fragile, due to:

* Differing versions of compilers/DWARF version result in a variety
    of breakages in the our code which analyzes the DWARF info;

* With musl, libunwind seems to be currently unable to traverse
    beyond signal handlers, due to the DWARF information not
    being present in the signal frame.
    See <https://maskray.me/blog/2022-04-10-unwinding-through-signal-handler>.
    Note that I have not verified that the problem in the blog
    post above is indeed what we're hitting, but it seems plausible.

cpp/core/Exception.cpp

@@ -4,12 +4,9 @@
 #include <atomic>
 #include <fcntl.h>
 #include <cxxabi.h>
-#define UNW_LOCAL_ONLY
-#include <libunwind.h>
 
 #include "Common.hpp"
 #include "BinaryFormatter.hpp"
-#include "Backtrace.hpp"
 #include "Exception.hpp"
 
 const char *translateErrno(int _errno) {
@@ -181,15 +178,6 @@ std::string removeTemplates(const std::string & s) {
 
 }
 
-AbstractException::AbstractException() {
-    generateBacktrace(_stacktrace, sizeof(_stacktrace));
-}
-
-
-const char * AbstractException::getStackTrace() const {
-    return _stacktrace;
-}
-
 const char *EggsException::what() const throw() {
     return _msg.c_str();
 }