What procedure might help remove or reduce this scar tissue?

If indeed, the "hard feeling" is believed to be scar tissue resulting from the repeated injections over many years performed in that area, then the use of intralesional anti-inflammatory injections can be considered to shrink and loosen the scar tissue. You would be wise to consult with an experienced, board certified cosmetic dermatologist to discuss this approach, as it is very important to inject just the right anti-inflammatory agent or combination of agents, in the proper concentrations and amounts, so as to avoid the atrophy and skin dimpling. Hope this helps and best of luck.