Replace clang-format with uncrustify

LLVM/clang is not used for any compilation due to it not supporting the
8-bit architectures we use (MCS-51, AVR). This means we are effectively
installing 250+ MiB of dependencies for a C formatting tool.

Replace it with uncrustify, which uses only ~600 KiB of space and has
more granular control of formatting (800+ options).

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/arch/avr/uart.c

@@ -6,7 +6,6 @@
 #include <arch/uart.h>
 #include <board/cpu.h>
 
-// clang-format off
 #define UART(N) \
     { \
         &UCSR ## N ## A, \
@@ -40,7 +39,6 @@
 #else
     #error "Could not find UART definitions"
 #endif
-// clang-format on
 
 int16_t uart_count(void) {
     return sizeof(UARTS) / sizeof(struct Uart);