Thank you for your question, David.  Removing the burned flowers and their petals because of sun scorch is really an aesthetic issue.  They're as unsightly because of sun as they are because of natural aging.  I would suggest, however, that you not remove any plant tissue below the flower. By pruning deeper, you leave open spaces from which water can evaporate, and may encourage new growth of leaves, which stand a good chance of being scorched themselves in this hot, dry summer.  You might want to consider covering the shrubs with a reflective material if the temperature returns to the 80 degree level.  Good luck!