Linux Mint’s grub has been installed in MBR ( /dev/sda )
Fedora’s grub has been installed in /dev/sda1 ( = /boot )
overwrite MBR’s grub with Fedora’s.
on Fedora , issue grub2-install
|Fedora# grub2-install /dev/sda|
After issuing grub2-install , Fefora’s grub will be installed in MBR ( in this case , /dev/sda )
You could boot both Fedora and Linux Mint after overwriting MBR’s grub with Fedora’s.