cmSystemTools: Drop unused CollapseCombinedPath method

All call sites have been converted to `CollapseFullPath`, so the
now-unused `CollapseCombinedPath` can be removed.

Fixes: #19050

Source/cmSystemTools.cxx

@@ -1510,36 +1510,6 @@ std::string cmSystemTools::ForceToRelativePath(std::string const& local_path,
   return relative;
 }
 
-std::string cmSystemTools::CollapseCombinedPath(std::string const& dir,
-                                                std::string const& file)
-{
-  if (dir.empty() || dir == ".") {
-    return file;
-  }
-
-  std::vector<std::string> dirComponents;
-  std::vector<std::string> fileComponents;
-  cmSystemTools::SplitPath(dir, dirComponents);
-  cmSystemTools::SplitPath(file, fileComponents);
-
-  if (fileComponents.empty()) {
-    return dir;
-  }
-  if (!fileComponents[0].empty()) {
-    // File is not a relative path.
-    return file;
-  }
-
-  std::vector<std::string>::iterator i = fileComponents.begin() + 1;
-  while (i != fileComponents.end() && *i == ".." && dirComponents.size() > 1) {
-    ++i;                      // Remove ".." file component.
-    dirComponents.pop_back(); // Remove last dir component.
-  }
-
-  dirComponents.insert(dirComponents.end(), i, fileComponents.end());
-  return cmSystemTools::JoinPath(dirComponents);
-}
-
 #ifdef CMAKE_BUILD_WITH_CMAKE
 bool cmSystemTools::UnsetEnv(const char* value)
 {

Source/cmSystemTools.h

@@ -374,12 +374,6 @@ public:
   static std::string ForceToRelativePath(std::string const& local_path,
                                          std::string const& remote_path);
 
-  /** Joins two paths while collapsing x/../ parts
-   * For example CollapseCombinedPath("a/b/c", "../../d") results in "a/d"
-   */
-  static std::string CollapseCombinedPath(std::string const& dir,
-                                          std::string const& file);
-
 #ifdef CMAKE_BUILD_WITH_CMAKE
   /** Remove an environment variable */
   static bool UnsetEnv(const char* value);