We can now make use of @available throughout our codebase.
We support Xcode 9 and up, which includes the iOS 11 SDK. This means we can remove any guards for SDKs prior to iOS 11.
This was cleaned up by running a global find-and-replace with the following regular expression:
```
Find:#if defined\(__IPHONE_11_0\) && \(__IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_11_0\)\n(.+if \(@available\(iOS 11.0, \*\)\) \{(?:.|\n)*?)(?:#else(?:.|\n)*?)?\n#endif
Replace:$1
```
With some additional cleanup for stragglers that didn't match this pattern. Note that else clauses were intentionally dropped.
Closes https://github.com/material-components/material-components-ios/issues/4909