You can see the upload methods available by running the following SQL query on the Gallery 2 database:
SELECT g_implId, g_orderWeight FROM g2_FactoryMap WHERE g_classType = 'ItemAddPlugin';
You can remove any you don't want or change the orderWeight to order the tabs (lower numbers come first). When you are done, you must flush the database cache in Site Admin -> Maintenance. Note that upgrades will reset these changes.
Original information from the forum post Limiting the upload methods.
There is an alternative method to remove core plugins by editing the code.
