powermgmt: Remove CURRENT_USB

CURRENT_USB overrides CURRENT_NORMAL when USB is plugged.
It defaults to 2 mA and wasn't defined on any target, but
this doesn't make sense to me. After all, the current
drawn by the CPU or other components won't change just
because USB was plugged in.

As far as I can tell, the only side effect of removing
this is reducing the estimated USB charging current.
This might mean CURRENT_MAX_CHG should be increased by
CURRENT_NORMAL on some (all?) targets to compensate,
but I'm not sure which targets would be affected.

Change-Id: I5aa5c3893ae1e4ce6b8803ab4e8c897d534eb08f

firmware/export/powermgmt.h

@@ -84,13 +84,6 @@ enum shutdown_type
 /* Start up power management thread */
 void powermgmt_init(void) INIT_ATTR;
 
-/* Generic current values that are intentionally meaningless - config header
- * should define proper numbers.*/
-
-#ifndef CURRENT_USB
-#define CURRENT_USB       2 /* usual current in mA in USB mode */
-#endif
-
 #if CONFIG_CHARGING && !defined(CURRENT_MAX_CHG)
 #define CURRENT_MAX_CHG   350  /* maximum charging current */
 #endif

firmware/powermgmt.c

@@ -190,18 +190,6 @@ int battery_current(void)
     int current = CURRENT_NORMAL;
 
 #ifndef BOOTLOADER
-    if (usb_inserted()
-#ifdef HAVE_USB_POWER
-    #if (CURRENT_USB < CURRENT_NORMAL)
-       || usb_powered_only()
-    #else
-       && !usb_powered_only()
-    #endif
-#endif
-    ) {
-        current = CURRENT_USB;
-    }
-
 #if defined(HAVE_BACKLIGHT) && defined(CURRENT_BACKLIGHT)
     if (backlight_get_current_timeout() == 0) /* LED always on */
         current += CURRENT_BACKLIGHT;