Example Podfile:

target 'MyProject' do
    pod 'AWSS3'
    pod 'RealmSwift'
end

and if you wanted to remove RealmSwift, remove that line from your Podfile

target 'MyProject' do
    pod 'AWSS3'
end

then from the command line run

$ pod install

and CocoaPods will remove RealmSwift.