[kernel] Remove old unused crti/crtn

These were never used because clang generates .ctors and .dtors instead
of .init and .fini

src/kernel/crti.s

@@ -1,14 +0,0 @@
-section .init
-global _init:function
-_init:
-	push rbp
-	mov rbp, rsp
-	; Control flow falls through to other .init sections
-
-section .fini
-global _fini:function
-_fini:
-	push rbp
-	mov rbp, rsp
-	; Control flow falls through to other .fini sections
-

src/kernel/crtn.s

@@ -1,10 +0,0 @@
-section .init
-	; Control flow falls through to here from other .init sections
-	pop rbp
-	ret
-
-section .fini
-	; Control flow falls through to here from other .fini sections
-	pop rbp
-	ret
-