Simplify detecting class properties to improve detection for anonymous classes

[sirbrillig]

Currently this sniff allows class properties to be unused without a warning. To determine if a variable it finds is a class property, it performs several checks; first it looks for a visibility keyword (eg: public) as the previous token. If that exists, then we assume it is a property. If that isn't found, it looks for a static keyword preceded by a visibility keyword. If there is no static, then it assumes there is no property access. If there is a static, we repeat the check for the visibility keyword. If there is a static token but no visibility keyword, we instead look to see if we are inside a class definition but not inside a function. If that is true, then we are a class property.

This logic is causing some problems for typed properties inside anonymous classes because the type keyword(s) are interfering with finding the visibility keyword. We can fix this by looking more carefully for the visibility keyword, like so:

		$startOfStatement = $phpcsFile->findPrevious([T_SEMICOLON, T_OPEN_CURLY_BRACKET], $stackPtr - 1);
		$stopAtPtr = is_bool($startOfStatement) ? 1 : $startOfStatement;
		$visibilityPtr = $phpcsFile->findPrevious($propertyDeclarationKeywords, $stackPtr - 1, $stopAtPtr > 0 ? $stopAtPtr : 0);

But that doesn't totally solve the problem for anonymous classes and I realized that we probably don't need to do it anyway. The last check that looks to see if we are inside a class definition but outside a function should be enough to find any property.

This PR removes all the logic described above and leaves only the final check.

Fixes #332

[jrfnl]

Won't this run foul for method parameters (which are within a class and not within a function scope) ?

[sirbrillig]

Won't this run foul for method parameters (which are within a class and not within a function scope) ?

I think it's safe because we look for function parameters before we look for class properties.