Cleanup unused options (#9115)

platformio.ini

 
 [platformio]
 src_dir = Marlin
-envs_dir = .pioenvs
+build_dir = .pioenvs
 lib_dir = .piolib
 libdeps_dir = .piolibdeps
 env_default = megaatmega2560
 platform    = atmelavr
 framework   = arduino
 board       = megaatmega2560
-build_flags = ${common.build_flags} -I $BUILDSRC_DIR
+build_flags = ${common.build_flags}
 board_f_cpu = 16000000L
 lib_deps    = ${common.lib_deps}
 src_filter  = ${common.default_src_filter}
 platform    = atmelavr
 framework   = arduino
 board       = megaatmega1280
-build_flags = ${common.build_flags} -I $BUILDSRC_DIR
+build_flags = ${common.build_flags}
 board_f_cpu = 16000000L
 lib_deps    = ${common.lib_deps}
 src_filter  = ${common.default_src_filter}
 platform    = atmelsam
 framework   = arduino
 board       = due
-build_flags = ${common.build_flags} -I $BUILDSRC_DIR
+build_flags = ${common.build_flags}
 lib_deps    = ${common.lib_deps}
 lib_ignore  = TMC26XStepper
 src_filter  = ${common.default_src_filter}
 platform    = atmelavr
 framework   = arduino
 board       = reprap_rambo
-build_flags = ${common.build_flags} -I $BUILDSRC_DIR
+build_flags = ${common.build_flags}
 board_f_cpu = 16000000L
 lib_deps    = ${common.lib_deps}
 src_filter  = ${common.default_src_filter}
 platform      = teensy
 framework     = arduino
 board         = teensy20pp
-build_flags   = ${common.build_flags} -I $BUILDSRC_DIR
+build_flags   = ${common.build_flags}
 #board_f_cpu  = 20000000L     ; Bug in Arduino framework disallows boards running at 20Mhz
 lib_deps      = ${common.lib_deps}
 lib_ldf_mode  = deep+
 platform    = teensy
 framework   = arduino
 board       = teensy35
-build_flags = ${common.build_flags} -I $BUILDSRC_DIR
+build_flags = ${common.build_flags}
 lib_deps    = ${common.lib_deps}
 lib_ignore  = Adafruit NeoPixel
 src_filter  = ${common.default_src_filter}