Cleanup chrono includes

With Ubuntu 22.04 GitHub runner image 20221119.2 there appears to be
some libclang difference so that include-what-you-use newly started
suggesting `bits/chrono` instead of `chrono` (which is spurious);
nevertheless, some of the uses of `#include <chrono>` indeed were
unnecessary.

Fixes: diffblue#7383

Author: tautschnig

src/goto-checker/bmc_util.h

@@ -12,7 +12,7 @@ Author: Daniel Kroening, Peter Schrammel
 #ifndef CPROVER_GOTO_CHECKER_BMC_UTIL_H
 #define CPROVER_GOTO_CHECKER_BMC_UTIL_H
 
-#include <chrono>
+#include <chrono> // IWYU pragma: keep
 #include <memory>
 
 #include <goto-symex/build_goto_trace.h>

src/goto-checker/multi_path_symex_checker.cpp

@@ -11,8 +11,6 @@ Author: Daniel Kroening, Peter Schrammel
 
 #include "multi_path_symex_checker.h"
 
-#include <chrono>
-
 #include <util/ui_message.h>
 
 #include <goto-symex/solver_hardness.h>

src/goto-checker/multi_path_symex_only_checker.cpp

@@ -16,8 +16,6 @@ Author: Daniel Kroening, Peter Schrammel
 #include <goto-symex/show_program.h>
 #include <goto-symex/show_vcc.h>
 
-#include <chrono>
-
 #include "bmc_util.h"
 
 multi_path_symex_only_checkert::multi_path_symex_only_checkert(

src/goto-checker/single_loop_incremental_symex_checker.cpp

@@ -13,8 +13,6 @@ Author: Daniel Kroening, Peter Schrammel
 
 #include "single_loop_incremental_symex_checker.h"
 
-#include <chrono>
-
 #include <util/structured_data.h>
 
 #include <goto-symex/slice.h>

src/goto-checker/single_path_symex_checker.h

@@ -12,8 +12,6 @@ Author: Daniel Kroening, Peter Schrammel
 #ifndef CPROVER_GOTO_CHECKER_SINGLE_PATH_SYMEX_CHECKER_H
 #define CPROVER_GOTO_CHECKER_SINGLE_PATH_SYMEX_CHECKER_H
 
-#include <chrono>
-
 #include "goto_symex_property_decider.h"
 #include "goto_trace_provider.h"
 #include "single_path_symex_only_checker.h"

src/goto-checker/single_path_symex_only_checker.cpp

@@ -11,8 +11,6 @@ Author: Daniel Kroening, Peter Schrammel
 
 #include "single_path_symex_only_checker.h"
 
-#include <chrono>
-
 #include <util/ui_message.h>
 
 #include <goto-symex/path_storage.h>

src/goto-checker/symex_coverage.cpp

@@ -24,7 +24,6 @@ Date: March 2016
 #include <linking/static_lifetime_init.h>
 
 #include <chrono>
-#include <ctime>
 #include <fstream> // IWYU pragma: keep
 #include <iostream>