Remove the unused `-Z trans-time-graph` flag.
Remove the unused `-Z trans-time-graph` flag.

Rebase of #50783 has accidentally revived the flag (which should be
renamed to `-Z codegen-time-graph` by #50615).

graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust