change log recovery to generic device_recovery_start function

Remove (or at least stop calling) the HTC-specific mechanism for
preserving the recovery log from before a radio or hboot update.
Replace it with a generic device_recovery_start() function which each
device's code can implement to do whatever it wants on recovery
startup.

Change-Id: If3cca4b498c0b1cf0565236404ecf56a1fc46123
diff --git a/default_recovery_ui.c b/default_recovery_ui.c
index d4e6204..409d679 100644
--- a/default_recovery_ui.c
+++ b/default_recovery_ui.c
@@ -29,6 +29,10 @@
                        "wipe cache partition",
                        NULL };
 
+int device_recovery_start() {
+    return 0;
+}
+
 int device_toggle_display(volatile char* key_pressed, int key_code) {
     return key_code == KEY_HOME;
 }