res_rtp_asterisk: Revert DTLS negotiation changes.

Due to locking issues within pjnath these changes are being
reverted until pjnath can be changed.

ASTERISK-25645

Revert "res_rtp_asterisk.c: Fix DTLS negotiation delays."

This reverts commit 24ae124e.

Change-Id: I2986cfb2c43dc14455c1bcaf92c3804f9da49705

Revert "res_rtp_asterisk: Resolve further timing issues with DTLS negotiation"

This reverts commit 965a0eee.

Change-Id: Ie68fafde27dad4b03cb7a1e27ce2a8502c3f7bbe