I notice that the Reference in NCBI "Recently" changed to the notation that you mentioned! There is a way for conversion, but I believe downloading each chromosome from UCSC then join them together is a better solution "Which is use".
download Major chromosome "Chr1-22 + X, Y, and MT" only, then use cat command on Linux/Mac OS terminal to concatenate all chromosomes in the same order. "Ex: cat Chr1.fa.gz Chr2.fa.gz .... ChrMT.fa.gz > Homo_sapiens_Hg19.fa.gz".
Now you have your reference genome and you can use it.