I'd like to remove rEFInd, since my laptop doesn't wake up from suspension (provided that the laptop is only powered by battery) anymore eversince I installed it (in neither of the operating systems: Mac OS and Ubuntu).

Assuming one has installed rEFInd on the main hard drive, then according to rEFInd's page it should be enough to remove (important: also empty the trash) the following folder:

/EFI/refind

http://www.rodsbooks.com/refind/installing.html#uninstalling

Indeed my blessed folder is that one:

Mac:~ user$ bless --info
finderinfo[0]: XXXXXXXX => Blessed System Folder is /EFI/refind
finderinfo[1]: XXXXXXXX => Blessed System File is /EFI/refind/refind_x64.efi
finderinfo[2]:      0 => Open-folder linked list empty
finderinfo[3]:      0 => No alternate OS blessed file/folder
finderinfo[4]:      0 => Unused field unset
finderinfo[5]: XXXXXXXX => OS X blessed folder is /EFI/refind
64-bit VSDB volume id:  0xXXXXXXXXXXXXXXXXXXXX
Mac:~ user$ bless --info --getBoot
/dev/disk0s2

Now my question is, do I have to remove just the refind folder, or also the EFI folder? Since my EFI folder also contains a tools folder. Here's the entire folder tree:

EFI
   - refind
       - icons
       - keys
       - refind_x64.efi
       - refind.conf
   - tools
       - gptsync_x63.efi