Revert "target: add target->type->has_mmu fn"

This patch introduced a bug preventing flash writes from working
on Cortex-M3 targets like the STM32.  Moreover, it's the wrong
approach for handling no-MMU targets.

The right way to handle no-MMU targets is to provide accessors
for physical addresses, and use them everywhere; and any code
which tries to work with virtual-to-physical mappings should use
a identity mapping (which can be defaulted).

And ... we can tell if a target has an MMU by seeing if it's
got an mmu() method.  No such methood means no MMU.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/target/cortex_m3.c

@@ -56,12 +56,6 @@ extern uint8_t armv7m_gdb_dummy_cpsr_value[];
 extern reg_t armv7m_gdb_dummy_cpsr_reg;
 #endif
 
-static int cortex_m3_has_mmu(struct target_s *target, bool *has_mmu)
-{
-	*has_mmu = false;
-	return ERROR_OK;
-}
-
 static int cortexm3_dap_read_coreregister_u32(swjdp_common_t *swjdp,
 		uint32_t *value, int regnum)
 {
@@ -1998,6 +1992,5 @@ target_type_t cortexm3_target =
 	.register_commands = cortex_m3_register_commands,
 	.target_create = cortex_m3_target_create,
 	.init_target = cortex_m3_init_target,
-	.has_mmu = cortex_m3_has_mmu,
 	.examine = cortex_m3_examine,
 };