kernel: remove duplicate definitions of k_thread stack and entry

Both k_thread_stack_t and (*k_thread_entry_t) are defined in
include/kernel.h and include/sys/arch_interface.h. The latter is
indirectly included by kernel.h which causes issues with some
toolchains. So remove the definitions in kernel.h.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

include/kernel.h

diff --git a/include/kernel.h b/include/kernel.h
index d809305..251079c 100644
--- a/include/kernel.h
+++ b/include/kernel.h
@@ -368,7 +368,13 @@
 struct __packed _k_thread_stack_element {
 	char data;
 };
-typedef struct _k_thread_stack_element k_thread_stack_t;
+
+/**
+ * @typedef k_thread_stack_t
+ * @brief Typedef of struct _k_thread_stack_element
+ *
+ * @see _k_thread_stack_element
+ */
 
 /**
  * @typedef k_thread_entry_t
@@ -388,7 +394,6 @@
  *
  * @return N/A
  */
-typedef void (*k_thread_entry_t)(void *p1, void *p2, void *p3);
 
 #ifdef CONFIG_THREAD_MONITOR
 struct __thread_entry {