Re-enable tsan.swift and witness_table_lookup.swift test on Linux, which is now passing after r345174 (#20036)

Author: kubamracek

test/Sanitizers/tsan.swift

@@ -9,9 +9,6 @@
 // don't support TSan.
 // UNSUPPORTED: remote_run
 
-// https://bugs.swift.org/browse/SR-6622
-// XFAIL: linux
-
 #if os(macOS) || os(iOS)
 import Darwin
 #elseif os(Linux) || os(FreeBSD) || os(PS4) || os(Android) || os(Cygwin)

validation-test/Sanitizers/witness_table_lookup.swift

@@ -4,9 +4,6 @@
 // REQUIRES: stress_test
 // REQUIRES: tsan_runtime
 
-// https://bugs.swift.org/browse/SR-6622
-// XFAIL: linux
-
 // Check that TSan does not report spurious races in witness table lookup.
 
 func consume(_ x: Any) {}