Remove erb_syntax pre-commit hook

It doesn't work as intended, and all the cool kids are using Haml.

Fixes: https://github.com/causes/overcommit/issues/13

Change-Id: I4bf355ae267b78042e71b780d8edb966b48c78bb
Reviewed-on: https://gerrit.causes.com/27376
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Greg Hurrell <greg@causes.com>