don't bother exporting kernel_execve()

most of the architectures don't and there's not a single
caller outside of core kernel.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/arm/kernel/sys_arm.c

@@ -120,7 +120,6 @@ int kernel_execve(const char *filename,
  out:
 	return ret;
 }
-EXPORT_SYMBOL(kernel_execve);
 
 /*
  * Since loff_t is a 64 bit type we avoid a lot of ABI hassle

arch/hexagon/kernel/syscall.c

@@ -87,4 +87,3 @@ int kernel_execve(const char *filename,
 
 	return retval;
 }
-EXPORT_SYMBOL(kernel_execve);

arch/unicore32/kernel/sys.c

@@ -104,7 +104,6 @@ int kernel_execve(const char *filename,
  out:
 	return ret;
 }
-EXPORT_SYMBOL(kernel_execve);
 
 /* Note: used by the compat code even in 64-bit Linux. */
 SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len,