alpha: Remove arch-specific strncpy() implementation

strncpy() has no remaining callers in the kernel[1]. Remove the
alpha-specific assembly implementation and __HAVE_ARCH_STRNCPY define,
falling back to the generic version in lib/string.c.

The __stxncpy helper (stxncpy.S/ev6-stxncpy.S) is retained as it is
still used by strncat.

Link: https://github.com/KSPP/linux/issues/90 [1]
Signed-off-by: Kees Cook <kees@kernel.org>

arch/alpha/include/asm/string.h

@@ -47,8 +47,6 @@ extern inline void *__memset(void *s, int c, size_t n)
 
 #define __HAVE_ARCH_STRCPY
 extern char * strcpy(char *,const char *);
-#define __HAVE_ARCH_STRNCPY
-extern char * strncpy(char *, const char *, size_t);
 #define __HAVE_ARCH_STRCAT
 extern char * strcat(char *, const char *);
 #define __HAVE_ARCH_STRNCAT

arch/alpha/lib/strncpy.S

@@ -1,83 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * arch/alpha/lib/strncpy.S
- * Contributed by Richard Henderson (rth@tamu.edu)
- *
- * Copy no more than COUNT bytes of the null-terminated string from
- * SRC to DST.  If SRC does not cover all of COUNT, the balance is
- * zeroed.
- *
- * Or, rather, if the kernel cared about that weird ANSI quirk.  This
- * version has cropped that bit o' nastiness as well as assuming that
- * __stxncpy is in range of a branch.
- */
-#include <linux/export.h>
-	.set noat
-	.set noreorder
-
-	.text
-
-	.align 4
-	.globl strncpy
-	.ent strncpy
-strncpy:
-	.frame $30, 0, $26
-	.prologue 0
-
-	mov	$16, $0		# set return value now
-	beq	$18, $zerolen
-	unop
-	bsr	$23, __stxncpy	# do the work of the copy
-
-	unop
-	bne	$18, $multiword	# do we have full words left?
-	subq	$24, 1, $3	# nope
-	subq	$27, 1, $4
-
-	or	$3, $24, $3	# clear the bits between the last
-	or	$4, $27, $4	# written byte and the last byte in COUNT
-	andnot	$3, $4, $4
-	zap	$1, $4, $1
-
-	stq_u	$1, 0($16)
-	ret
-
-	.align	4
-$multiword:
-	subq	$27, 1, $2	# clear the final bits in the prev word
-	or	$2, $27, $2
-	zapnot	$1, $2, $1
-	subq	$18, 1, $18
-
-	stq_u	$1, 0($16)
-	addq	$16, 8, $16
-	unop
-	beq	$18, 1f
-
-	nop
-	unop
-	nop
-	blbc	$18, 0f
-
-	stq_u	$31, 0($16)	# zero one word
-	subq	$18, 1, $18
-	addq	$16, 8, $16
-	beq	$18, 1f
-
-0:	stq_u	$31, 0($16)	# zero two words
-	subq	$18, 2, $18
-	stq_u	$31, 8($16)
-	addq	$16, 16, $16
-	bne	$18, 0b
-
-1:	ldq_u	$1, 0($16)	# clear the leading bits in the final word
-	subq	$24, 1, $2
-	or	$2, $24, $2
-
-	zap	$1, $2, $1
-	stq_u	$1, 0($16)
-$zerolen:
-	ret
-
-	.end	strncpy
-	EXPORT_SYMBOL(strncpy)

arch/alpha/lib/styncpy.S

@@ -1,4 +1,3 @@
-#include "strncpy.S"
 #ifdef CONFIG_ALPHA_EV67
 #include "ev67-strncat.S"
 #else