Rename closeDialog to cleanupSession

The current name of SipDelegate[Connection]#closeDialog assumes
there will only be one SIP dialog per SIP session and does not
adequately cover the case where a SIP INVITE has forked and
generated multiple dialogs for the same call-id.

Instead, rename closeDialog to cleanupSession, which is more
accurate and should be called after all SIP dialogs associated
with the SIP session represented by the call-id have closed.

Bug: 184858064
Test: atest CtsTelephonyTestCases
Change-Id: I438dbc45dffbaf33e0cf36ddc61008fd8c18209c