[trace-dump] Fix MemFree writing to file for mem_profile feature

[dblnz]

The trace-dump utility tool expects only a pointer when a free operation is reported.
The place where the mem_trace file is read can be checked at trace_dump/main.rs#L593 where you can see that for frame_id==3 there is no amount read.

When mem_trace feature is enabled for both host and guest, this works as follows:

• the guest makes a VMExit for each Alloc/Free.
• It passes ptr, len to the host for the alloc/free which represent: the allocated/freed pointer, the length of the allocated memory
• The host then unwinds the stack (using the shared memory) to re-construct the call tree for the specific allocation.
• It writes to a <uuid>.trace file the following info: time, trace_id, ptr, amount, stack. Trace ID represents the type of allocation.
• The tool expects only ptr, stack for the Free variant, hence the fix here.
• The trace_dump tool takes the debug symbols file as a parameter to know how to translate the pointers of the stack frames.
• It the lists all the operations listed in the <uuid>.trace file