Remove unused `grunt-html-minify`

It add grunt task `html_minify`, which was not used anywhere.
This module require old Grunt `~0.4.1` and with this module
grunt cannot be upgraded to newer versions

build/package.json

@@ -7,7 +7,6 @@
     "lodash": "^4.0.0",
     "grunt": "0.4.5",
     "grunt-replace": "0.7.3",
-    "grunt-html-minify": "0.3.1",
     "grunt-text-replace": "0.3.11",
     "mocha": "1.18.2",
     "chai": "1.9.1",