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

Change-Id: If3cca4b498c0b1cf0565236404ecf56a1fc46123
diff --git a/recovery_ui.h b/recovery_ui.h
index 8818ef3..e451bdf 100644
--- a/recovery_ui.h
+++ b/recovery_ui.h
@@ -17,6 +17,9 @@
 #ifndef _RECOVERY_UI_H
 #define _RECOVERY_UI_H
+// Called when recovery starts up.  Returns 0.
+extern int device_recovery_start();
 // Called in the input thread when a new key (key_code) is pressed.
 // *key_pressed is an array of KEY_MAX+1 bytes indicating which other
 // keys are already pressed.  Return true if the text display should