Update debuggerd to use libbacktrace.

Remove all of the code in debuggerd that uses libcorkscrew directly
and replace with libbacktrace.

Also do a bit of refactoring to clean up some functions that were
passing around variables that weren't used.

Bug: 8410085

Change-Id: I27da4fbe3f12ce38a85b4432fc1119984c9c391b