Drop the dependency on AB_OTA_UPDATER flag.

This shortens the gap between A/B and non-A/B builds, by replacing the
dependency on build-time flag with runtime detection instead. It also
allows building and testing both paths regardless of the target OTA
type.

The size increase to /sbin/recovery looks negligible (< 0.01%).
 - marlin: increased from 2084928 to 2085024;
 - angler: increased from 2084776 to 2084896.

Test: Run recovery_component_test on angler and marlin.
Test: Sideload an A/B OTA package on marlin.
Test: Sideload a non-A/B OTA package on angler.
Change-Id: I1d927d1ede9713fb42f73b4fe324aa5705ee6f99
diff --git a/otautil/paths.cpp b/otautil/paths.cpp
index f08e51c..33ab4a5 100644
--- a/otautil/paths.cpp
+++ b/otautil/paths.cpp
@@ -23,6 +23,7 @@
 constexpr const char kDefaultStashDirectoryBase[] = "/cache/recovery";
 constexpr const char kDefaultTemporaryInstallFile[] = "/tmp/last_install";
 constexpr const char kDefaultTemporaryLogFile[] = "/tmp/recovery.log";
+constexpr const char kDefaultTemporaryUpdateBinary[] = "/tmp/update-binary";
 
 Paths& Paths::Get() {
   static Paths paths;
@@ -36,4 +37,5 @@
       resource_dir_(kDefaultResourceDirectory),
       stash_directory_base_(kDefaultStashDirectoryBase),
       temporary_install_file_(kDefaultTemporaryInstallFile),
-      temporary_log_file_(kDefaultTemporaryLogFile) {}
+      temporary_log_file_(kDefaultTemporaryLogFile),
+      temporary_update_binary_(kDefaultTemporaryUpdateBinary) {}