Remove irrelevant @throws annotations

[morozov]

Q	A
Type	improvement

At the time of its introduction in #4746, Comparator::columnsEqual() was annotated with @throws Exception because the following code flow could result in one: Comparator::columnsEqual() → AbstractPlatform::columnsEqual() → AbstractPlatform::getColumnDeclarationSQL() → AbstractPlatform::getInlineColumnCommentSQL(). The last method in the chain would throw an exception if the platform didn't support inline column comments.

As of #5727, the NotSupported exception is declared as unchecked (extends LogicException), so this code path no longer throws a checked exception. In fact, this makes the Comparator API free of checked exceptions.

Additionally, declaring NoColumnsSpecifiedForTable as unchecked allows removing most of the @throws annotations from the Platform API. The remaining @throws is related to the type registry and is out of the scope of this change.

Note that the recent versions of PHPStan support analyzing the @throws (see Bring your exceptions under control with @throws). We may want to use them on CI in the future.