Use ro.build.fingerprint instead of ro.bootimage.*

ro.bootimage.* sysprops will be removed as they are redundant. Read
ro.build.fingerprint instead.

This is safe because:
2) ro.bootimage.build.fingerprint is the same as other
ro.<partition>.build.fingerprint all of which are from
$(BUILD_FINGERPRINT_FILE).
3) BUILD_FINGERPRINT_FILE is composed of PRODUCT_BRAND, TARGET_PRODUCT,
TARGET_DEVICE, etc.
4) ro.build.fingerprint is auto-composed by init at runtime by the same
rule as #3.

Bug: 117892318
Test: enter into the recovery mode and manually inspect the title line
Change-Id: If28d710f45b98a0effc0159851bca6afb2aa5735
diff --git a/recovery.cpp b/recovery.cpp
index b1f106b..e02bc72 100644
--- a/recovery.cpp
+++ b/recovery.cpp
@@ -702,7 +702,7 @@
   }
 
   std::vector<std::string> title_lines =
-      android::base::Split(android::base::GetProperty("ro.bootimage.build.fingerprint", ""), ":");
+      android::base::Split(android::base::GetProperty("ro.build.fingerprint", ""), ":");
   title_lines.insert(std::begin(title_lines), "Android Recovery");
   ui->SetTitle(title_lines);