Revert "Promote PromCon 2017 CfP"

This reverts commit b66ec14a.

The PromCon 2017 CfP is closed now.

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-  Share your experiences with Prometheus at PromCon 2017!&nbsp;&nbsp;—&nbsp;&nbsp;<a href="https://promcon.io/2017-munich/submit/">Submit a talk</a>
+  CloudNativeCon 2017 videos are out!&nbsp;&nbsp;—&nbsp;&nbsp;<a href="https://www.youtube.com/watch?v=uV_sh7_lVw8&list=PLqm7NmbgjUExeDZU8xb2nxz-ysnjuC2Mz&index=1">Watch the Prometheus track here</a>
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