Remove dependency on submodule 'framework'

ESP_IDF dose not have support for recursive updation of submodules, also
it has no dependency on submodule 'framework' currently.
Therefore, this commit eliminates the dependency on the 'framework' submodule.

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "framework"]
-	path = framework
-	url = https://github.com/Mbed-TLS/mbedtls-framework

CMakeLists.txt

@@ -298,11 +298,6 @@ if(LIB_INSTALL_DIR)
     set(CMAKE_INSTALL_LIBDIR "${LIB_INSTALL_DIR}")
 endif()
 
-if (NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/framework/CMakeLists.txt")
-    message(FATAL_ERROR "${CMAKE_CURRENT_SOURCE_DIR}/framework/CMakeLists.txt not found. Run `git submodule update --init` from the source tree to fetch the submodule contents.")
-endif()
-add_subdirectory(framework)
-
 add_subdirectory(include)
 
 add_subdirectory(3rdparty)