Shrink flash and RAM usage even more (#627)

Remove MIDI support from the core's main TinyUSB.  MIDI is still supported
using the Adafruit TinyUSB library, just like before (the core never
did use it).

Compile the Pico-SDK using `-Os`

Remove unneeded warning in UF2 upload

Blink.ino shows a savings of 3.5KB flash and 400 bytes of RAM.

For comparison, with this PR blink.ino reports:
````
Sketch uses 49908 bytes (3%) of program storage space. Maximum is 1568768 bytes.
Global variables use 7024 bytes (2%) of dynamic memory, leaving 255120 bytes for local variables. Maximum is 262144 bytes.
````

As comparison, using the MBED core blink.ino reports:
````
Sketch uses 78882 bytes (0%) of program storage space. Maximum is 16777216 bytes.
Global variables use 42780 bytes (15%) of dynamic memory, leaving 227556 bytes for local variables. Maximum is 270336 bytes.
````

So, with this PR we use **37% less flash** and and **87% less RAM**
for simple sketches.

tools/libpico/CMakeLists.txt

@@ -21,6 +21,7 @@ target_compile_definitions(pico PUBLIC
 
 target_compile_options(pico PUBLIC
 	-fno-exceptions
+	-Os
 	$<$<COMPILE_LANGUAGE:CXX>:-fno-rtti>
 )
 

tools/libpico/tusb_config.h

@@ -73,7 +73,7 @@
 #define CFG_TUD_HID              (2)
 #define CFG_TUD_CDC              (1)
 #define CFG_TUD_MSC              (0)
-#define CFG_TUD_MIDI             (1)
+#define CFG_TUD_MIDI             (0)
 #define CFG_TUD_VENDOR           (0)
 
 #define CFG_TUD_CDC_RX_BUFSIZE  (256)

tools/uf2conv.py

@@ -350,7 +350,7 @@ def main():
                     ser = serial.Serial(args.serial, 1200)
                     ser.dtr = False
                 except:
-                    print("Caught exception during reset!")
+                    pass # Ignore error in the case it is already in upload mode
             except:
                 pass
     if args.list: