Remove some deadcode (#11034)

* chore: remove empty handleWebResponse() stub in PiWebServer

* chore: remove unused PowerStatus::knowsUSB()

* chore: remove orphaned fsListFiles() declaration

* chore: remove stale #if 0 SPI-comms test in SX126xInterface

* chore: remove stale #if 0 cert-delete debug block in WebServer

src/PowerStatus.h

@@ -51,9 +51,6 @@ class PowerStatus : public Status
 
     bool getHasUSB() const { return hasUSB == OptTrue; }
 
-    /// Can we even know if this board has USB power or not
-    bool knowsUSB() const { return hasUSB != OptUnknown; }
-
     bool getIsCharging() const { return isCharging == OptTrue; }
 
     int getBatteryVoltageMv() const { return batteryVoltageMv; }