zephyr: Remove outdated workaround for Kinetis

Remove this workaround.  The Kinetis flash driver has supported
FLASH_PAGE_LAYOUT since at least January 2018.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/boot/zephyr/include/target.h b/boot/zephyr/include/target.h
index a11616f..f7d2d0f 100644
--- a/boot/zephyr/include/target.h
+++ b/boot/zephyr/include/target.h
@@ -24,15 +24,6 @@
 #define FLASH_ALIGN FLASH_WRITE_BLOCK_SIZE
 
 /*
- * TODO: remove soc_family_kinetis.h once its flash driver supports
- * FLASH_PAGE_LAYOUT.
- */
-#if defined(CONFIG_SOC_FAMILY_KINETIS)
-#include "soc_family_kinetis.h"
-#endif
-#endif /* !defined(MCUBOOT_TARGET_CONFIG) */
-
-/*
  * Sanity check the target support.
  */
 #if (!defined(CONFIG_XTENSA) && !defined(DT_FLASH_DEV_NAME)) || \
diff --git a/boot/zephyr/targets/soc_family_kinetis.h b/boot/zephyr/targets/soc_family_kinetis.h
deleted file mode 100644
index ab60e09..0000000
--- a/boot/zephyr/targets/soc_family_kinetis.h
+++ /dev/null
@@ -1,8 +0,0 @@
-/*
- * Copyright (c) 2017 Linaro
- * SPDX-License-Identifier: Apache-2.0
- */
-
-#ifdef CONFIG_SOC_SERIES_KINETIS_K6X
-#define FLASH_AREA_IMAGE_SECTOR_SIZE	0x01000
-#endif