Remove unused variable

Removed unused `is_param` variable for symbol.

Closes RustPython#1879

compiler/src/symboltable.rs

@@ -95,7 +95,6 @@ pub struct Symbol {
     pub name: String,
     // pub table: SymbolTableRef,
     pub scope: SymbolScope,
-    pub is_param: bool,
     pub is_referenced: bool,
     pub is_assigned: bool,
     pub is_parameter: bool,
@@ -108,7 +107,6 @@ impl Symbol {
             name: name.to_owned(),
             // table,
             scope: SymbolScope::Unknown,
-            is_param: false,
             is_referenced: false,
             is_assigned: false,
             is_parameter: false,