pcie_i2c: cleanup headers

Cleanup headers by dropping unused ones and adding missing ones.

Tested: Only ran unit-tests.
Change-Id: I64ee6164e7de0295226c399b0f03d67bba34554f
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/pcie_i2c.cpp b/pcie_i2c.cpp
index 6f93d01..5f45650 100644
--- a/pcie_i2c.cpp
+++ b/pcie_i2c.cpp
@@ -21,10 +21,9 @@
 
 #include <cstdint>
 #include <cstring>
-#include <sstream>
 #include <string>
-#include <system_error>
-#include <unordered_map>
+#include <tuple>
+#include <vector>
 
 namespace google
 {