all: remove .cvsignore files

Rename following .cvsignore files to .gitkeep since they are
required by the build (directories must exist before build):
	- bin/fossil/.gitkeep
	- bin/fs/.gitkeep
	- bin/venti/.gitkeep

Change-Id: I9c2865058480cffb3a4613f25e2eca1f7e5578c0

bin/venti/.cvsignore

@@ -1,21 +0,0 @@
-buildindex
-checkarenas
-checkindex
-clumpstats
-copy
-findscore
-fixarenas
-fmtarenas
-fmtbloom
-fmtindex
-fmtisect
-mirrorarenas
-printarena
-rdarena
-read
-sync
-syncindex
-venti
-verifyarena
-wrarena
-write