[lldb][NFCI] Remove unused struct ConstString::StringIsEqual

This doesn't seem to be used at all, no need to keep it around.

Author: bulbazord

lldb/include/lldb/Utility/ConstString.h

@@ -78,22 +78,6 @@ class ConstString {
   ///     from \a cstr.
   explicit ConstString(const char *cstr, size_t max_cstr_len);
 
-  /// C string equality binary predicate function object for ConstString
-  /// objects.
-  struct StringIsEqual {
-    /// C equality test.
-    ///
-    /// Two C strings are equal when they are contained in ConstString objects
-    /// when their pointer values are equal to each other.
-    ///
-    /// \return
-    ///     Returns \b true if the C string in \a lhs is equal to
-    ///     the C string value in \a rhs, \b false otherwise.
-    bool operator()(const char *lhs, const char *rhs) const {
-      return lhs == rhs;
-    }
-  };
-
   /// Convert to bool operator.
   ///
   /// This allows code to check a ConstString object to see if it contains a