Don't save symbol library when importing Altium schematic.

The user can always export the symbol library from
the schematic if they want it.

This also improves performance by more than 100X
in the test case for #20299.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/15468

eeschema/sch_io/altium/sch_io_altium.cpp

@@ -1071,9 +1071,6 @@ void SCH_IO_ALTIUM::ParseFileHeader( const ALTIUM_COMPOUND_FILE& aAltiumSchFile
         fixupSymbolPinNameNumbers( symbol.second );
         fixupSymbolPinNameNumbers( libSymbolIt->second );
 
-        m_pi->SaveSymbol( getLibFileName().GetFullPath(),
-                          new LIB_SYMBOL( *( libSymbolIt->second ) ), m_properties.get() );
-
         symbol.second->SetLibSymbol( libSymbolIt->second );
     }
 
@@ -1181,9 +1178,6 @@ void SCH_IO_ALTIUM::ParseASCIISchematic( const wxString& aFileName )
         fixupSymbolPinNameNumbers( symbol.second );
         fixupSymbolPinNameNumbers( libSymbolIt->second );
 
-        m_pi->SaveSymbol( getLibFileName().GetFullPath(),
-                          new LIB_SYMBOL( *( libSymbolIt->second ) ), m_properties.get() );
-
         symbol.second->SetLibSymbol( libSymbolIt->second );
     }
 
@@ -3685,7 +3679,6 @@ void SCH_IO_ALTIUM::ParsePowerPort( const std::map<wxString, wxString>& aPropert
         libSymbol->GetValueField().SetPosition( valueFieldPos );
 
         // this has to be done after parsing the LIB_SYMBOL!
-        m_pi->SaveSymbol( getLibFileName().GetFullPath(), libSymbol, m_properties.get() );
         m_powerSymbols.insert( { symName, libSymbol } );
     }