Revert "exclude serial module for T-Echo, saves 3000 bytes"

This reverts commit 38347fa6db.

variants/t-echo/variant.h

@@ -206,9 +206,6 @@ External serial flash WP25R1635FZUIL0
 // To debug via the segger JLINK console rather than the CDC-ACM serial device
 // #define USE_SEGGER
 
-// T-Echo does not have a free serial port for this module
-#define MESHTASTIC_EXCLUDE_SERIAL 1
-
 // Battery
 // The battery sense is hooked to pin A0 (4)
 // it is defined in the anlaolgue pin section of this file