$ sudo apt-get remove gdb64 

Uninstall gdb64 including dependent package

If you would like to remove gdb64 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove gdb64 

Use Purging gdb64

If you use with purge options to gdb64 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge gdb64 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove gdb64 

See Also,