Don't remove wifi preferences when updating AP to avoid GC.

import android.support.v7.preference.Preference;

import android.support.v7.preference.PreferenceViewHolder;

import android.text.Spannable;

import android.text.TextUtils;

import android.text.style.TextAppearanceSpan;

import android.util.Log;

import android.view.ContextMenu;

import android.widget.TextView;

import android.widget.TextView.BufferType;

import android.widget.Toast;

import com.android.internal.logging.MetricsLogger;

import com.android.internal.logging.MetricsProto.MetricsEvent;

import com.android.settings.LinkifyUtils;

                // AccessPoints are automatically sorted with TreeSet.

                final Collection<AccessPoint> accessPoints =

                        mWifiTracker.getAccessPoints();

                getPreferenceScreen().removeAll();

                boolean hasAvailableAccessPoints = false;

                int index = 0;

                    // Ignore access points that are out of range.

                    if (accessPoint.getLevel() != -1) {

                        String key = accessPoint.getBssid();

                        if (TextUtils.isEmpty(key)) {

                            key = accessPoint.getSsidStr();

                        }

                        hasAvailableAccessPoints = true;

                        LongPressAccessPointPreference pref = (LongPressAccessPointPreference)

                                getCachedPreference(key);