[musicdb] drop filename CRC from the songview - it's not used for anything useful, and the filename is indexed anyway
[musicdb] drop setting of unused strKaraLyrFileCRC column in karaokedata table
[dbwrappers] drop unused ComputeCRC() function
[musicdb] NULL out entries in the song, karaokedata and album tables that are no longer used.
Merge pull request #4604 from jmarshallnz/drop_file_crc

Drop file crc from music database