[clang] Remove unused lambda capture (NFC)

/llvm-project/clang/lib/Basic/Targets/X86.cpp:1368:23:
error: lambda capture 'this' is not used [-Werror,-Wunused-lambda-capture]
  auto getPriority = [this](StringRef Feature) -> unsigned {
                      ^~~~
1 error generated.

clang/lib/Basic/Targets/X86.cpp

@@ -1365,7 +1365,7 @@ static llvm::X86::ProcessorFeatures getFeature(StringRef Name) {
 }
 
 unsigned X86TargetInfo::getFMVPriority(ArrayRef<StringRef> Features) const {
-  auto getPriority = [this](StringRef Feature) -> unsigned {
+  auto getPriority = [](StringRef Feature) -> unsigned {
     // Valid CPUs have a 'key feature' that compares just better than its key
     // feature.
     using namespace llvm::X86;