res_sorcery_realtime: Remove leading ^ requirement.

res_sorcery_realtime's search-by-regex callback performed a check to
ensure that the passed-in regex began with a caret (^). If it did not,
then no results would be returned.

This callback only started to become used when "like" support was added
to PJSIP CLI commands. The CLI command for listing objects would pass an
empty regex ("") to the sorcery backend if no "like" statement was
present. For most sorcery backends, this resulted in returning all
objects. However, for realtime, this resulted in returning no objects.

This commit seeks to fix the regression by removing the requirement from
res_sorcery_realtime for the passed-in-regex to begin with a caret.

ASTERISK-25689 #close
Reported by Marcelo Terres

Change-Id: I22b4dc5d7f3f11bb29ac2e42ef94682e9bab3b20