Remove Linkedin button

"A [vitality curve](http://en.wikipedia.org/wiki/Vitality_curve) is a construct whereby a workforce is graded in accordance with the individual productivity of its members ... The "top 20" percent of the workforce is most productive, and 70% (the "vital 70") work adequately. The other "bottom 10" are nonproducers and should be fired."

Over 90 days,

- facebook - 39.2%
- twitter - 36.2%
- g-plus - 8.1%
- linkedin - 4.1%

/cc @kungpochicken