Remove redundant rubygem-ffi

The rubygem-ffi component is already added in all of the other top-level
projects:

    $ git grep rubygem-ffi configs/projects/
    configs/projects/_pdk-components.rb:proj.component 'rubygem-ffi'
    configs/projects/_shared-pe-bolt-server.rb:proj.component('rubygem-ffi')
    configs/projects/_shared-pe-bolt-server_with_ruby.rb:proj.component('rubygem-ffi')
    configs/projects/_shared-pe-installer-runtime.rb:proj.component('rubygem-ffi')
    configs/projects/agent-runtime-7.x.rb:  proj.component 'rubygem-ffi'
    configs/projects/agent-runtime-main.rb:  proj.component 'rubygem-ffi'
    configs/projects/bolt-runtime.rb:  proj.component 'rubygem-ffi'

configs/projects/_shared-agent-components.rb

@@ -63,7 +63,6 @@
 
 if platform.is_windows? || platform.is_solaris? || platform.is_aix?
   proj.component 'rubygem-minitar'
-  proj.component 'rubygem-ffi'
 end
 
 if platform.is_macos?