Improve some comments of strings and codes

1) Correct improper function comment about forget menu
2) Extends char limit of wifi_scan_always_turn_on_message_unknown for
translation.
3) Correct string comment on Saved networks summary

Bug: 130628569
Test: make RunSettingsRoboTests -j32 ROBOTEST_FILTER=com.android.settings.wifi.WifiSettingsTest
Change-Id: I0e60e4f205c794367dfffc032cb4334dac4d1cdd