Remove several ignore rules

The main purpose of this change is to avoid a problem where new golden
files added to certain directories for test purposes (like .log)
shouldn't be ignored.

Cleaning up a bit more and broadening the definition, this removes
ignore rules for artifacts of Terraform itself (state files, plans).
It's generally not recommended to be using this codebase as your
Terraform working directory anyway; build here, test elsewhere.

.gitignore

 *.dll
 *.exe
 .DS_Store
-example.tf
-terraform.tfplan
-terraform.tfstate
 bin/
 modules-dev/
 /pkg/
@@ -13,9 +10,6 @@ website/build
 website/node_modules
 .vagrant/
 *.backup
-./*.tfstate
-.terraform/
-*.log
 *.bak
 *~
 .*.swp
@@ -27,9 +21,5 @@ website/node_modules
 website/vendor
 vendor/
 
-# Test exclusions
-!command/testdata/**/*.tfstate
-!command/testdata/**/.terraform/
-
 # Coverage
 coverage.txt