remove unnecessary quoting

platformio.ini

@@ -27,7 +27,7 @@ board = nodemcuv2
 lib_deps =
   ${common.lib_deps_builtin}
   ${common.lib_deps_external}
-build_flags = ${common.build_flags} -D FIRMWARE_VARIANT="nodemcuv2"
+build_flags = ${common.build_flags} -D FIRMWARE_VARIANT=nodemcuv2
 
 [env:d1_mini]
 platform = espressif8266
@@ -36,13 +36,13 @@ board = d1_mini
 lib_deps =
   ${common.lib_deps_builtin}
   ${common.lib_deps_external}
-build_flags = ${common.build_flags} -D FIRMWARE_VARIANT="d1_mini"
+build_flags = ${common.build_flags} -D FIRMWARE_VARIANT=d1_mini
 
 [env:esp12]
 platform = espressif8266
 board = esp12e
 framework = arduino
-build_flags = ${common.build_flags} -Wl,-Tesp8266.flash.4m1m.ld -D FIRMWARE_VARIANT="esp12"
+build_flags = ${common.build_flags} -Wl,-Tesp8266.flash.4m1m.ld -D FIRMWARE_VARIANT=esp12
 lib_deps =
   ${common.lib_deps_builtin}
   ${common.lib_deps_external}
@@ -51,7 +51,7 @@ lib_deps =
 platform = espressif8266
 board = esp07
 framework = arduino
-build_flags = ${common.build_flags} -Wl,-Tesp8266.flash.1m64.ld -D FIRMWARE_VARIANT="esp07"
+build_flags = ${common.build_flags} -Wl,-Tesp8266.flash.1m64.ld -D FIRMWARE_VARIANT=esp07
 lib_deps =
   ${common.lib_deps_builtin}
   ${common.lib_deps_external}