libuzfs: remove definitions set by configure for kernel

uzfs should be configured with --with-config=user to disable kernel
interfaces check and thus no kernel interfaces definitions will be
set in configure.

HAVE_D_PRUNE_ALIASES is an exception that zfs relies on which is set in
configure, so we need to define it manually.

include/sys/kernel.h

@@ -294,7 +294,7 @@ extern int fls(int x);
 
 #define	time_before(a, b)	time_after(b, a)
 
-#undef HAVE_SINGLE_SHRINKER_CALLBACK
+#define HAVE_D_PRUNE_ALIASES
 
 // zfs_ioctl.c
 #define	FKIOCTL				0x80000000
@@ -310,12 +310,4 @@ extern gid_t crgetfsgid(const cred_t *cr);
 // libzfs
 extern long uzfs_ioctl(unsigned cmd, unsigned long arg);
 
-#undef HAVE_TMPFILE
-#undef HAVE_INODE_TIMESPEC64_TIMES
-#undef HAVE_SPLIT_SHRINKER_CALLBACK
-#undef HAVE_SINGLE_SHRINKER_CALLBACK
-#undef HAVE_SUPER_SETUP_BDI_NAME
-#undef CONFIG_USER_NS
-#undef HAVE_VFS_IOV_ITER
-
 #endif	/* _SYS_KERNEL_H */