Fix build error on Pie with TW_NO_LEGACY_PROPS := true

Fixes:
bootable/recovery/twinstall.cpp:83:12: error: unused function 'switch_to_legacy_properties' [-Werror,-Wunused-function]
static int switch_to_legacy_properties()
           ^
bootable/recovery/twinstall.cpp:110:12: error: unused function 'switch_to_new_properties' [-Werror,-Wunused-function]
static int switch_to_new_properties()
           ^
bootable/recovery/twinstall.cpp:176:13: error: unused function 'update_binary_has_legacy_properties' [-Werror,-Wunused-function]
static bool update_binary_has_legacy_properties(const char *binary) {
            ^
3 errors generated.

Change-Id: Ie30fd7ae74b00e791100572b49a17ff638212e5a
diff --git a/twinstall.cpp b/twinstall.cpp
index a2f54c9..f451ca5 100644
--- a/twinstall.cpp
+++ b/twinstall.cpp
@@ -67,10 +67,12 @@
 
 #define AB_OTA "payload_properties.txt"
 
+#ifndef TW_NO_LEGACY_PROPS
 static const char* properties_path = "/dev/__properties__";
 static const char* properties_path_renamed = "/dev/__properties_kk__";
 static bool legacy_props_env_initd = false;
 static bool legacy_props_path_modified = false;
+#endif
 
 enum zip_type {
 	UNKNOWN_ZIP_TYPE = 0,
@@ -79,6 +81,7 @@
 	TWRP_THEME_ZIP_TYPE
 };
 
+#ifndef TW_NO_LEGACY_PROPS
 // to support pre-KitKat update-binaries that expect properties in the legacy format
 static int switch_to_legacy_properties()
 {
@@ -120,6 +123,7 @@
 
 	return 0;
 }
+#endif
 
 static int Install_Theme(const char* path, ZipWrap *Zip) {
 #ifdef TW_OEM_BUILD // We don't do custom themes in OEM builds
@@ -173,6 +177,7 @@
 	return INSTALL_SUCCESS;
 }
 
+#ifndef TW_NO_LEGACY_PROPS
 static bool update_binary_has_legacy_properties(const char *binary) {
 	const char str_to_match[] = "ANDROID_PROPERTY_WORKSPACE";
 	int len_to_match = sizeof(str_to_match) - 1;
@@ -205,6 +210,7 @@
 
 	return found;
 }
+#endif
 
 static int Run_Update_Binary(const char *path, ZipWrap *Zip, int* wipe_cache, zip_type ztype) {
 	int ret_val, pipe_fd[2], status, zip_verify;