fix(validations): remove input invalid style.

[emoralesb05]

Description

Since [email protected] will have the invalid state, there is no more need for it.

What's included?

• Removal of invalid state css in _input.scss.

Test Steps

• ng serve
• `See required invalid inputs still turn red.

General Tests for Every PR

• ng serve --aot still works.
• npm run lint passes.
• npm test passes and code coverage is not lower.
• npm run build still works.

[emoralesb05]

This should be merged/reviewed after material has been upgraded to beta.3

[emoralesb05]

Closing since we will do this change in the beta.3 upgrade.