Renaming a couple of poorly named player OST's

*Changed the vague OST equates "layer" and "layer_plus" to the more accurate and descriptive name "top_solid_bit", and "lrb_solid_bit", as named in the Sonic 3k disassembly, which also removes repetition of the word "layer".

*Changed the RAM constants to "Saved_layer" and "Saved_layer_2P" to have new fitting names "Saved_Solid_bits" and "Saved_Solid_bits_2P".