Remove FEATURE_LWIP. The LwIP stack is enabled on all builds now

Leave the FEATURE_LWIP enabled in build scripts so that it does
not break any builds.

Removed 'feature_add: ["LWIP"]' on all targets.

doxyfile_options

@@ -845,7 +845,7 @@ EXCLUDE_PATTERNS       = */tools/* \
                          */features/mbedtls/* \
                          */features/storage/* \
                          */features/unsupported/* \
-                         */features/FEATURE_LWIP/* \
+                         */features/lwipstack/* \
                          */features/FEATURE_UVISOR/* \
                          */features/nanostack/sal-stack-nanostack/* \
                          */features/nanostack/coap-service/* \

doxygen_options.json

@@ -4,11 +4,11 @@
     "MACRO_EXPANSION": "YES",
     "EXPAND_ONLY_PREDEF": "NO",
     "SEARCH_INCLUDES": "YES",
-    "INCLUDE_PATH": "", 
-    "INCLUDE_FILE_PATTERNS": "", 
+    "INCLUDE_PATH": "",
+    "INCLUDE_FILE_PATTERNS": "",
     "PREDEFINED": "DOXYGEN_ONLY DEVICE_ANALOGIN DEVICE_ANALOGOUT DEVICE_CAN DEVICE_CRC DEVICE_ETHERNET DEVICE_EMAC DEVICE_FLASH  DEVICE_I2C DEVICE_I2CSLAVE DEVICE_I2C_ASYNCH DEVICE_INTERRUPTIN DEVICE_ITM DEVICE_LPTICKER DEVICE_PORTIN DEVICE_PORTINOUT DEVICE_PORTOUT DEVICE_PWMOUT DEVICE_RTC DEVICE_TRNG DEVICE_SERIAL DEVICE_SERIAL_ASYNCH DEVICE_SERIAL_FC DEVICE_SLEEP DEVICE_SPI DEVICE_SPI_ASYNCH DEVICE_SPISLAVE DEVICE_STORAGE \"MBED_DEPRECATED_SINCE(f, g)=\" \"MBED_ENABLE_IF_CALLBACK_COMPATIBLE(F, M)=\" \"MBED_DEPRECATED(s)=\"",
-    "EXPAND_AS_DEFINED": "", 
+    "EXPAND_AS_DEFINED": "",
     "SKIP_FUNCTION_MACROS": "NO",
     "STRIP_CODE_COMMENTS": "NO",
-    "EXCLUDE_PATTERNS": "*/tools/* */targets/* */features/mbedtls/* */features/storage/* */features/unsupported/* */BUILD/* */rtos/TARGET_CORTEX/rtx*/* */cmsis/* */features/FEATURE_LWIP/* */features/FEATURE_UVISOR/* */nanostack/sal-stack-nanostack/* */nanostack/coap-service/* */ble/generic/* */ble/pal/*  */mbed-trace/* */mbed-coap/* */nanostack-libservice/* */mbed-client-randlib/* */nanostack/sal-stack-nanostack-eventloop/*"
+    "EXCLUDE_PATTERNS": "*/tools/* */targets/* */features/mbedtls/* */features/storage/* */features/unsupported/* */BUILD/* */rtos/TARGET_CORTEX/rtx*/* */cmsis/* */features/lwipstack/* */features/FEATURE_UVISOR/* */nanostack/sal-stack-nanostack/* */nanostack/coap-service/* */ble/generic/* */ble/pal/*  */mbed-trace/* */mbed-coap/* */nanostack-libservice/* */mbed-client-randlib/* */nanostack/sal-stack-nanostack-eventloop/*"
 }

features/lwipstack/CONTRIBUTING.md

@@ -1,6 +1,6 @@
 # Description
 
-This document describes how to update the Arm Mbed OS LWIP stack. The Mbed OS LWIP stack is a copy of the LWIP master repository. Stack is located in `FEATURE_LWIP/lwip-interface/lwip` directory.
+This document describes how to update the Arm Mbed OS LWIP stack. The Mbed OS LWIP stack is a copy of the LWIP master repository. Stack is located in `features/lwipstack/lwip` directory.
 
 When you add new releases or single commits from the LWIP master repository, you must fetch them using the Mbed OS LWIP fork repository. Use the repository to rename LWIP source files with the `lwip_` prefix to make them compatible with the Mbed OS build system.
 
@@ -109,9 +109,9 @@ You can integrate a new release using the following steps.
 
 3. Do a subtree pull for LWIP prefixed branch in the Mbed OS root directory.
 
-    `git subtree pull --squash -P features/FEATURE_LWIP/lwip-interface/lwip <remote name> <new prefixed branch> -m "<commit message>"`
+    `git subtree pull --squash -P features/lwipstack/lwip <remote name> <new prefixed branch> -m "<commit message>"`
 
-    `e.g. git subtree pull --squash -P features/FEATURE_LWIP/lwip-interface/lwip lwip-fork mbed-os-lwip-stable-2_0_2-prefixed -m "Merged lwip 2.0.2 stable"`
+    `e.g. git subtree pull --squash -P features/lwipstack/lwip lwip-fork mbed-os-lwip-stable-2_0_2-prefixed -m "Merged lwip 2.0.2 stable"`
 
     After this step, there is a new commit visible in the Mbed OS master branch that contains the changes.