Longtime Channel 5 reporter-anchor Heather Unruh is leaving. In a terse statement to station employees Friday morning, WCVB-TV president and general manager Bill Fine said Unruh has decided to call it quits after 15 years. “[News director] Andrew [Vrees] and I want to sincerely thank Heather for her many contributions to WCVB, and the Boston community where she often offered her talents as an MC to raise money for some great non-profits,’’ Fine wrote. “We wish her all the best.’’ Unruh’s exit seemed inevitable after Maria Stephanos joined the station, taking over as coanchor of the 7 and 11 p.m. newscasts. Unruh had been coanchoring at 4:30 and 6 p.m. Not long after Fine’s memo went out, Unruh tweeted: “Friends . . . tonight I sign off for the last time on ch. 5. I am warmed by the kindness you have shown me. C U at 6pm’’ and added an Eleanor Roosevelt quote: “The future belongs to those who believe in the quality of their dreams.’’