Fix a warning

relfile.c: In function 'relfile_rw_record':
relfile.c:112:4: warning: implicit declaration of function 'memset'
[-Wimplicit-function-declaration]
    memset(buffer->buffer, 0, buffer->recordlen);
    ^
relfile.c:112:4: warning: incompatible implicit declaration of built-in
function 'memset' [enabled by default]
Clean up unused XS-1541 interrupt definitions