target-i386: drop usage of prev_debug_excp_handler

Chains of exception handlers are currently unused feature, drop it
for now so as not to expose prev_debug_excp_handler at global
scope when moving tcg initialization into target-i386/cpu.c

Later we probably could re-invent better interface for this.
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>

target-i386/helper.c

@@ -941,8 +941,6 @@ int check_hw_breakpoints(CPUX86State *env, int force_dr6_update)
     return hit_enabled;
 }
 
-static CPUDebugExcpHandler *prev_debug_excp_handler;
-
 static void breakpoint_handler(CPUX86State *env)
 {
     CPUBreakpoint *bp;
@@ -965,8 +963,6 @@ static void breakpoint_handler(CPUX86State *env)
                 break;
             }
     }
-    if (prev_debug_excp_handler)
-        prev_debug_excp_handler(env);
 }
 
 typedef struct MCEInjectionParams {
@@ -1166,8 +1162,7 @@ X86CPU *cpu_x86_init(const char *cpu_model)
         inited = 1;
         optimize_flags_init();
 #ifndef CONFIG_USER_ONLY
-        prev_debug_excp_handler =
-            cpu_set_debug_excp_handler(breakpoint_handler);
+        cpu_set_debug_excp_handler(breakpoint_handler);
 #endif
     }
     if (cpu_x86_register(cpu, cpu_model) < 0) {