[6.1] Remove the introduced: 6.0 argument from the to-be-deprecated attributes on #expect(performing:throws:) and #require(performing:throws:). (#889)

- **Explanation**: Fix spurious errors building with pre-6.0 language
modes when using `#expect(performing:throws:)` or
`#require(performing:throws:)`.
- **Scope**: Tests written in 5.x language mode that use the
to-be-deprecated expectation macros.
  - **Issues**: N/A
- **Original PRs**: #881
  - **Risk**: Low
  - **Testing**: Automated testing/tested at desk.
- **Reviewers**: @briancroom @stmontgomery @SeanROlszewski
@suzannaratcliff

Author: grynspan

Documentation/Proposals/0006-return-errors-from-expect-throws.md

@@ -105,7 +105,7 @@ is not statically available. The problematic overloads will also be deprecated:
 -) where E: Error & Equatable
 +) -> E where E: Error & Equatable
 
-+@available(swift, introduced: 6.0, deprecated: 100000.0, message: "Examine the result of '#expect(throws:)' instead.")
++@available(swift, deprecated: 100000.0, message: "Examine the result of '#expect(throws:)' instead.")
 +@discardableResult
  @freestanding(expression) public macro expect<R>(
    _ comment: @autoclosure () -> Comment? = nil,
@@ -115,7 +115,7 @@ is not statically available. The problematic overloads will also be deprecated:
 -)
 +) -> (any Error)?
 
-+@available(swift, introduced: 6.0, deprecated: 100000.0, message: "Examine the result of '#require(throws:)' instead.")
++@available(swift, deprecated: 100000.0, message: "Examine the result of '#require(throws:)' instead.")
 +@discardableResult
  @freestanding(expression) public macro require<R>(
    _ comment: @autoclosure () -> Comment? = nil,

Sources/Testing/Expectations/Expectation+Macro.swift

@@ -375,7 +375,7 @@ public macro require<R>(
 /// ``expect(throws:_:sourceLocation:performing:)-1hfms`` instead. If the thrown
 /// error need only equal another instance of [`Error`](https://developer.apple.com/documentation/swift/error),
 /// use ``expect(throws:_:sourceLocation:performing:)-7du1h`` instead.
-@available(swift, introduced: 6.0, deprecated: 100000.0, message: "Examine the result of '#expect(throws:)' instead.")
+@available(swift, deprecated: 100000.0, message: "Examine the result of '#expect(throws:)' instead.")
 @discardableResult
 @freestanding(expression) public macro expect<R>(
   _ comment: @autoclosure () -> Comment? = nil,
@@ -427,7 +427,7 @@ public macro require<R>(
 ///
 /// If `expression` should _never_ throw, simply invoke the code without using
 /// this macro. The test will then fail if an error is thrown.
-@available(swift, introduced: 6.0, deprecated: 100000.0, message: "Examine the result of '#require(throws:)' instead.")
+@available(swift, deprecated: 100000.0, message: "Examine the result of '#require(throws:)' instead.")
 @discardableResult
 @freestanding(expression) public macro require<R>(
   _ comment: @autoclosure () -> Comment? = nil,