kernel: remove obsolete slab tuning patch

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/generic/patches-3.18/900-slab_maxsize.patch

@@ -1,13 +0,0 @@
---- a/include/linux/slab.h
-+++ b/include/linux/slab.h
-@@ -172,8 +172,8 @@ size_t ksize(const void *);
-  * to do various tricks to work around compiler limitations in order to
-  * ensure proper constant folding.
-  */
--#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
--				(MAX_ORDER + PAGE_SHIFT - 1) : 25)
-+#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT - 1) <= 17 ? \
-+				(MAX_ORDER + PAGE_SHIFT - 1) : 17)
- #define KMALLOC_SHIFT_MAX	KMALLOC_SHIFT_HIGH
- #ifndef KMALLOC_SHIFT_LOW
- #define KMALLOC_SHIFT_LOW	5

target/linux/generic/patches-4.1/900-slab_maxsize.patch

@@ -1,13 +0,0 @@
---- a/include/linux/slab.h
-+++ b/include/linux/slab.h
-@@ -171,8 +171,8 @@ size_t ksize(const void *);
-  * to do various tricks to work around compiler limitations in order to
-  * ensure proper constant folding.
-  */
--#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
--				(MAX_ORDER + PAGE_SHIFT - 1) : 25)
-+#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT - 1) <= 17 ? \
-+				(MAX_ORDER + PAGE_SHIFT - 1) : 17)
- #define KMALLOC_SHIFT_MAX	KMALLOC_SHIFT_HIGH
- #ifndef KMALLOC_SHIFT_LOW
- #define KMALLOC_SHIFT_LOW	5

target/linux/generic/patches-4.4/900-slab_maxsize.patch

@@ -1,13 +0,0 @@
---- a/include/linux/slab.h
-+++ b/include/linux/slab.h
-@@ -189,8 +189,8 @@ size_t ksize(const void *);
-  * to do various tricks to work around compiler limitations in order to
-  * ensure proper constant folding.
-  */
--#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
--				(MAX_ORDER + PAGE_SHIFT - 1) : 25)
-+#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT - 1) <= 17 ? \
-+				(MAX_ORDER + PAGE_SHIFT - 1) : 17)
- #define KMALLOC_SHIFT_MAX	KMALLOC_SHIFT_HIGH
- #ifndef KMALLOC_SHIFT_LOW
- #define KMALLOC_SHIFT_LOW	5