This setting is now moved to the **Advanced settings** in General settings.
Max diff line count
Set the maximum size of diffs that is allowed to be displayed in the diff dialog. Setting this option to a higher value will affect diff display performance.
While the Git for Jira app uses default Jira System Encoding (utf-8) to deliver source files and diffs of repository, this setting is for those who have several repositories with source files encoded under different encodings.
More on general settings
Diff settings (this page)