Rename, clean up boards/variants (#21655)

* Consolidate variant scripts
* Rename Marlin-local boards
* Simplify variants where possible
* Rename variants
* CHITU_F103 and MEEB_3DP: Maple platform `platformio-build-stm32f1.py` uses the 'board' name, not 'board_build.variant' so folder names match 'board' and not `board_build.variant`.

buildroot/share/PlatformIO/scripts/STM32F103RC_fysetc.py

@@ -1,24 +1,11 @@
 #
-# STM32F103RC_fysetc.py
+# buildroot/share/PlatformIO/scripts/STM32F103RC_fysetc.py
 #
 import os
 from os.path import join
 from os.path import expandvars
 Import("env")
 
-# Relocate firmware from 0x08000000 to 0x08008000
-#for define in env['CPPDEFINES']:
-#    if define[0] == "VECT_TAB_ADDR":
-#        env['CPPDEFINES'].remove(define)
-#env['CPPDEFINES'].append(("VECT_TAB_ADDR", "0x08008000"))
-
-#custom_ld_script = os.path.abspath("buildroot/share/PlatformIO/ldscripts/fysetc_stm32f103rc.ld")
-#for i, flag in enumerate(env["LINKFLAGS"]):
-#    if "-Wl,-T" in flag:
-#        env["LINKFLAGS"][i] = "-Wl,-T" + custom_ld_script
-#    elif flag == "-T":
-#        env["LINKFLAGS"][i + 1] = custom_ld_script
-
 # Custom HEX from ELF
 env.AddPostAction(
 	join("$BUILD_DIR","${PROGNAME}.elf"),