SoftwareSerial destructor not complete

I tried to find a workaround for [this SoftwareSerial issue](https://github.com/arduino/ArduinoCore-renesas/issues/523) by dynamically creating & destroying instances via new & delete. However, after a few cycles the board stalls, i.e. no life-beat and manual reset required. Seems like the destructor does not release all required resources.

Here is a sketch to reproduce the error:

```
#include

SoftwareSerial *SoftSerial;

void setup() {
pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));

SoftSerial = new SoftwareSerial(0, 1); // Rx, Tx
SoftSerial->begin(9600);
SoftSerial->write(0x55);
delete(SoftSerial);

SoftSerial = new SoftwareSerial(0, 1); // Rx, Tx
SoftSerial->begin(19200);
SoftSerial->write(0x55);
delete(SoftSerial);

delay(500);
}

```

Start by reproducing the stall with the SoftwareSerial new/delete sketch provided in the issue, varying the baud-rate cycles as shown. Inspect the SoftwareSerial implementation and destructor to identify resources that survive deletion. Done means repeated construction, begin, write, and deletion no longer stalls the board or requires a manual reset.

Written by the indexing model from the issue text.