SoC: remove 2018 SoC material from the navbar

Author: chriscool

SoC-2018-Ideas.md

@@ -1,6 +1,7 @@
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 layout: default
 title: SoC 2018 Ideas
+navbar: false
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 This is the idea page for Summer of Code 2018 for Git.

SoC-2018-Microprojects.md

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 layout: default
 title: SoC 2018 Applicant Microprojects
+navbar: false
 ---
 
 ## Introduction

SoC-2018-Org-Application.md

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 layout: default
 title: SoC 2018 Organization Application
+navbar: false
 ---
 
 This is a draft of git's application to Google's Summer of Code 2018.