remove problematic rules

@brandyscarney says:

> here are the ones I ran into issues with in the framework:
>
> * `no-unnecessary-type-assertion` is throwing errors when we cast as an HTMLElement - which is necessary because otherwise it queries as an `Element` and throws errors that the properties don’t exist, this is a bug in TS: palantir/tslint#3540
> * `prefer-for-of` is throwing errors on node lists which is also a bug: palantir/tslint#2927
> * `no-conditional-assignment` is used in DOM controller

tslint.js

@@ -15,7 +15,6 @@ module.exports = {
     "jsdoc-format": [true, "check-multiline-start"],
     "linebreak-style": [true, "LF"],
     "new-parens": true,
-    "no-conditional-assignment": true,
     "no-debugger": true,
     "no-duplicate-super": true,
     "no-duplicate-switch-case": true,
@@ -32,7 +31,6 @@ module.exports = {
     "no-string-throw": true,
     "no-switch-case-fall-through": true,
     "no-trailing-whitespace": true,
-    "no-unnecessary-type-assertion": true,
     "no-unsafe-finally": true,
     "no-unused-variable": true,
     "no-var-keyword": true,
@@ -53,7 +51,6 @@ module.exports = {
     },
     "prefer-conditional-expression": true,
     "prefer-const": true,
-    "prefer-for-of": true,
     "quotemark": {"options": ["single"]},
     "radix": true,
     "semicolon": {"options": ["always"]},