refactor(md-dropdown): remove legacy fix

[vbornand]

Same as PR #461 and #462 but with correct convention and correct files.

As discussed in the issue #458 I've removed the legacy dropdown-fix. It was for an old version of materialize and not used by default.

Breaking changes:

• The method useDropdownFix doesn't exist anymore.

[Thanood]

I wonder if we should issue a warning if someone still uses .useDropdownFix(). Maybe just a simple console.warn in config-builder.js.

[vbornand]

Ok I add a warning

[vbornand]

What do you think of:
console.warn("The method useDropdownFix has no effect in this version and will be removed in a future version.");

[Thanood]

I like that. 😃