chore: Drop sass-spec testing

Was dropped in v5 branch before because this is better covered in libsass

Author: nschonni

package.json

@@ -79,9 +79,7 @@
     "mocha": "^3.1.2",
     "mocha-lcov-reporter": "^1.2.0",
     "object-merge": "^2.5.1",
-    "read-yaml": "^1.0.0",
     "rimraf": "^2.5.2",
-    "sass-spec": "https://github.com/sass/sass-spec.git#dc2d573",
     "unique-temp-dir": "^1.0.0"
   }
 }

scripts/coverage.js

@@ -55,8 +55,7 @@ function coverage() {
                  if (instrumentedfiles.length === sourcefiles.length) {
                    fs.readdirSync('test').filter(function(file){
                      return file.substr(-6)  === 'api.js' ||
-                            file.substr(-11) === 'runtime.js' ||
-                            file.substr(-7)  === 'spec.js';
+                            file.substr(-11) === 'runtime.js';
                    }).forEach(function(file){
                      mocha.addFile(
                        path.join('test', file)