fastboot: only require Linux modules on Linux

The following three modules aren't defined for Windows
builds:
 e2fsdroid mke2fs.conf sload_f2fs

Which leads to the following errors:
build/make/core/main.mk:586: warning: Missing required dependency host_cross_e2fsdroid from module host_cross_fastboot defined in system/core/fastboot/Android.mk
build/make/core/main.mk:586: warning: Missing required dependency host_cross_mke2fs.conf from module host_cross_fastboot defined in system/core/fastboot/Android.mk
build/make/core/main.mk:586: warning: Missing required dependency host_cross_sload_f2fs from module host_cross_fastboot defined in system/core/fastboot/Android.mk

Here, I've removed their requirement for the Windows build and
only included the requirement for the Linux build.

Bug: 7456955
Test: above errors no longer present
Change-Id: I14fdb880d868f893fa5899ea200820bd885a3bc1
diff --git a/fastboot/Android.mk b/fastboot/Android.mk
index dfcf090..f5bcc26 100644
--- a/fastboot/Android.mk
+++ b/fastboot/Android.mk
@@ -39,13 +39,15 @@
 LOCAL_MODULE_TAGS := debug
 LOCAL_MODULE_HOST_OS := darwin linux windows
 LOCAL_CFLAGS += -Wall -Wextra -Werror -Wunreachable-code
-LOCAL_REQUIRED_MODULES := mke2fs e2fsdroid mke2fs.conf make_f2fs sload_f2fs
+LOCAL_REQUIRED_MODULES := mke2fs make_f2fs
 
 LOCAL_SRC_FILES_linux := usb_linux.cpp
 LOCAL_STATIC_LIBRARIES_linux := libselinux
+LOCAL_REQUIRED_MODULES_linux := e2fsdroid mke2fs.conf sload_f2fs
 
 LOCAL_SRC_FILES_darwin := usb_osx.cpp
 LOCAL_STATIC_LIBRARIES_darwin := libselinux
+LOCAL_REQUIRED_MODULES_darwin := e2fsdroid mke2fs.conf sload_f2fs
 LOCAL_LDLIBS_darwin := -lpthread -framework CoreFoundation -framework IOKit -framework Carbon
 LOCAL_CFLAGS_darwin := -Wno-unused-parameter