[lldb][TypeSystemClang] CreateParameterDeclarations: don't specify SmallVector size

This was causing Ubuntu buildbot failures:
```
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp: In member function ‘llvm::SmallVector<clang::ParmVarDecl*> lldb_private::TypeSystemClang::CreateParameterDeclarations(clang::FunctionDecl*, const clang::FunctionProtoType&, const llvm::SmallVector<llvm::StringRef>&)’:
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp:7728:10: error: could not convert ‘params’ from ‘SmallVector<[...],12>’ to ‘SmallVector<[...],6>’
 7728 |   return params;
      |          ^~~~~~
      |          |
      |          SmallVector<[...],12>
```

It's unclear why 12 was chosen here. Given we don't set the
size in other places where we parse parameters, this patch
just removes the constant.

Author: Michael137

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

@@ -7710,7 +7710,7 @@ TypeSystemClang::CreateParameterDeclarations(
   assert(parameter_names.empty() ||
          parameter_names.size() == prototype.getNumParams());
 
-  llvm::SmallVector<clang::ParmVarDecl *, 12> params;
+  llvm::SmallVector<clang::ParmVarDecl *> params;
   for (unsigned param_index = 0; param_index < prototype.getNumParams();
        ++param_index) {
     llvm::StringRef name =