Avoid failing in syscall_mix for traces without syscall markers (#6440)

Removes the check for trace file type that fails for older traces that
do not have the syscall marker. It is better to simply report zero
counts than to fail with a fatal error.

clients/drcachesim/tools/syscall_mix.cpp

@@ -111,25 +111,14 @@ bool
 syscall_mix_t::parallel_shard_memref(void *shard_data, const memref_t &memref)
 {
     shard_data_t *shard = reinterpret_cast<shard_data_t *>(shard_data);
-    if (memref.marker.type != TRACE_TYPE_MARKER)
+    if (memref.marker.type != TRACE_TYPE_MARKER ||
+        memref.marker.marker_type != TRACE_MARKER_TYPE_SYSCALL)
         return true;
-    switch (memref.marker.marker_type) {
-    case TRACE_MARKER_TYPE_FILETYPE:
-        if (!TESTANY(OFFLINE_FILE_TYPE_SYSCALL_NUMBERS, memref.marker.marker_value)) {
-            shard->error = "Trace does not have TRACE_MARKER_TYPE_SYSCALL markers.";
-            return false;
-        }
-        break;
-    case TRACE_MARKER_TYPE_SYSCALL: {
-        int syscall_num = static_cast<int>(memref.marker.marker_value);
+    int syscall_num = static_cast<int>(memref.marker.marker_value);
 #ifdef X64
-        assert(static_cast<uintptr_t>(syscall_num) == memref.marker.marker_value);
+    assert(static_cast<uintptr_t>(syscall_num) == memref.marker.marker_value);
 #endif
-        ++shard->syscall_counts[syscall_num];
-        break;
-    }
-    default: break;
-    }
+    ++shard->syscall_counts[syscall_num];
     return true;
 }