Clean up include paths, remove duplicates/invalids (#229)

lib/platform_inc.txt

 -iwithprefixbefore/cores/rp2040/api/deprecated-avr-comp/
 -iwithprefixbefore/lib/pico_base/
--iwithprefixbefore/pico-examples/build/generated/pico_base
 -iwithprefixbefore/pico-extras/src/common/pico_audio/include
 -iwithprefixbefore/pico-extras/src/common/pico_util_buffer/include
 -iwithprefixbefore/pico-extras/src/rp2_common/pico_audio_i2s/include
 -iwithprefixbefore/pico-sdk/lib/tinyusb/src/
 -iwithprefixbefore/pico-sdk/src/boards/include
 -iwithprefixbefore/pico-sdk/src/common/pico_base/include
--iwithprefixbefore/pico-sdk/src/common/pico_base/include/
 -iwithprefixbefore/pico-sdk/src/common/pico_binary_info/include
 -iwithprefixbefore/pico-sdk/src/common/pico_bit_ops/include
 -iwithprefixbefore/pico-sdk/src/common/pico_divider/include
@@ -16,8 +14,6 @@
 -iwithprefixbefore/pico-sdk/src/common/pico_time/include
 -iwithprefixbefore/pico-sdk/src/common/pico_util/include
 -iwithprefixbefore/pico-sdk/src/rp2040/hardware_regs/include
--iwithprefixbefore/pico-sdk/src/rp2040/hardware_regs/include/
--iwithprefixbefore/pico-sdk/src/rp2040/hardware_regs/include/
 -iwithprefixbefore/pico-sdk/src/rp2040/hardware_structs/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/hardware_adc/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/hardware_base/include
@@ -37,7 +33,6 @@
 -iwithprefixbefore/pico-sdk/src/rp2_common/hardware_spi/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/hardware_sync/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/hardware_timer/include
--iwithprefixbefore/pico-sdk/src/rp2_common/hardware_timer/include/
 -iwithprefixbefore/pico-sdk/src/rp2_common/hardware_uart/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/hardware_vreg/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/hardware_watchdog/include
@@ -47,9 +42,7 @@
 -iwithprefixbefore/pico-sdk/src/rp2_common/pico_float/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/pico_int64_ops/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/pico_multicore/include
--iwithprefixbefore/pico-sdk/src/rp2_common/pico_multicore/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/pico_platform/include
--iwithprefixbefore/pico-sdk/src/rp2_common/pico_platform/include/
 -iwithprefixbefore/pico-sdk/src/rp2_common/pico_printf/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/pico_runtime/include
 -iwithprefixbefore/pico-sdk/src/rp2_common/pico_stdio/include