[MC] Remove deprecated lookupTarget overload (#196778)

This has been deprecated for a while and was slated for removal after
the branching of LLVM 22. Remove it since I'm on on the Google integrate
rotation this week and can take care of any failures on our end.

llvm/include/llvm/MC/TargetRegistry.h

diff --git a/llvm/include/llvm/MC/TargetRegistry.h b/llvm/include/llvm/MC/TargetRegistry.h
index f7ecc71..b111342 100644
--- a/llvm/include/llvm/MC/TargetRegistry.h
+++ b/llvm/include/llvm/MC/TargetRegistry.h
@@ -725,17 +725,6 @@
 
   /// lookupTarget - Lookup a target based on a target triple.
   ///
-  /// \param TripleStr - The triple to use for finding a target.
-  /// \param Error - On failure, an error string describing why no target was
-  /// found.
-  // TODO(boomanaiden154): Remove this function after LLVM 22 branches.
-  [[deprecated("Use overload accepting Triple instead")]]
-  static const Target *lookupTarget(StringRef TripleStr, std::string &Error) {
-    return lookupTarget(Triple(TripleStr), Error);
-  }
-
-  /// lookupTarget - Lookup a target based on a target triple.
-  ///
   /// \param Triple - The triple to use for finding a target.
   /// \param Error - On failure, an error string describing why no target was
   /// found.