You can drive this pin from your MCU directly.
Page 5 of the datasheet, section PIN FUNCTIONS, reads literally:
SHDN (Pin 8 ): Shutdown. When this pin is at ground the LTC1261L operates normally. An internal 5μA pull-down keeps SHDN low if it is left floating. When SHDN is pulled high, the LTC1261L enters shutdown mode. In shutdown, the charge pump is disabled, the output collapses to 0V and the quiescent current drops to 5μA typically.