public round_start(Handle:event, const String:name[], bool:dontBroadcast)
{
     ServerCommand("sv_cheats 1;ent_remove_all prop_dynamic;sv_cheats 0");
}

report_entities   
Class: ai_network (1)
Class: cs_gamerules (1)
Class: cs_player_manager (1)
Class: cs_team_manager (4)
Class: func_breakable (1)
Class: func_button (1)
Class: func_buyzone (1)
Class: func_door (10)
Class: info_player_counterterrorist (22)
Class: info_player_terrorist (22)
Class: info_teleport_destination (2)
Class: player (1)
Class: point_template (1)
Class: predicted_viewmodel (2)
Class: prop_dynamic (1)
Class: scene_manager (1)
Class: soundent (1)
Class: trigger_once (1)
Class: trigger_teleport (3)
Class: worldspawn (1)
Total 78 entities (0 empty, 77 edicts)

#include <sourcemod>

public OnPluginStart()
{
     HookEvent("round_start", round_start, EventHookMode_PostNoCopy);
}

public round_start(Handle:event, const String:name[], bool:dontBroadcast)
{
     ServerCommand("sv_cheats 1;ent_remove_all prop_dynamic;sv_cheats 0");
}

ServerCommand("sv_cheats 1;ent_remove_all prop_dynamic;sv_cheats 0");