Remove string copy

Changed 'ecma_copy_or_ref_ecma_string' to 'ecma_ref_ecma_string'. It does
not copy the string if the maximum number of reference counter is reached,
but bails out with an error like the 'ecma_ref_object' function does.

JerryScript-DCO-1.0-Signed-off-by: László Langó llango.u-szeged@partner.samsung.com

jerry-core/ecma/base/ecma-helpers-value.c

@@ -637,7 +637,7 @@ ecma_copy_value (ecma_value_t value)  /**< value description */
     }
     case ECMA_TYPE_STRING:
     {
-      return ecma_make_string_value (ecma_copy_or_ref_ecma_string (ecma_get_string_from_value (value)));
+      return ecma_make_string_value (ecma_ref_ecma_string (ecma_get_string_from_value (value)));
     }
     case ECMA_TYPE_OBJECT:
     {