Remove include of backtrace/Backtrace.h.

Somehow the code was still including this include from libbacktrace.
I think the libbacktrace include directory was coming from some
transitive includes. I verified that nothing in debuggerd is using
the libbacktace.so shared library.

Bug: 120606663

Test: Builds, unit tests pass.
Change-Id: I85c2837c5a539ccefc5a7140949988058d21697a
Merged-In: I85c2837c5a539ccefc5a7140949988058d21697a
(cherry picked from commit 3336c7bce087d33cc9ab0b02139b39551539f8a6)
diff --git a/debuggerd/libdebuggerd/tombstone.cpp b/debuggerd/libdebuggerd/tombstone.cpp
index 4bdb9c8..4c1d633 100644
--- a/debuggerd/libdebuggerd/tombstone.cpp
+++ b/debuggerd/libdebuggerd/tombstone.cpp
@@ -27,6 +27,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/mman.h>
 #include <sys/ptrace.h>
 #include <sys/stat.h>
 #include <time.h>