flash: Remove pic32_flash.c

As the only pic32 platform does not enable flash, this is dead code.
Remove it.

Cc: Purna Chandra Mandal <purna.mandal@microchip.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/boot/Kconfig b/boot/Kconfig
index 59d0c65..1503739 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -486,7 +486,7 @@
 config HAVE_SYS_MONITOR_BASE
 	bool
 	depends on ARC || MIPS || M68K || NIOS2 || PPC || XTENSA || X86 \
-		|| FLASH_PIC32 || ENV_IS_IN_FLASH || MTD_NOR_FLASH
+		|| ENV_IS_IN_FLASH || MTD_NOR_FLASH
 	depends on !EFI_APP
 	default y