Remove `CertificateValidationException`'s dependency on the Android SDK

import javax.net.ssl.SSLHandshakeException;

import android.security.KeyChainException;

public class CertificateValidationException extends MessagingException {

    public static final long serialVersionUID = -1;

    private final Reason mReason;

        while (throwable != null

                && !(throwable instanceof CertPathValidatorException)

                && !(throwable instanceof CertificateException)

                && !(throwable instanceof KeyChainException)

                && !("android.security.KeyChainException".equals(throwable.getClass().getCanonicalName()))

                && !(throwable instanceof SSLHandshakeException)) {

            throwable = throwable.getCause();

        }