[docs] Removed mention of polarssl (obsolete)

README.rst

@@ -238,8 +238,6 @@ There are 4 variants of *openwisp-config*:
 - **openwisp-config-openssl**: depends on *ca-certificates* and *libopenssl*
 - **openwisp-config-mbedtls**: depends on *ca-certificates* and *libmbedtls*
 - **openwisp-config-cyassl**: depends on *ca-certificates* and *libcyassl*
-- **openwisp-config-polarssl**: depends on *ca-certificates* and *libpolarssl* (**note**: polarssl
-  has been deprecated in favour of mbedtls on more recent OpenWRT versions)
 - **openwisp-config-nossl**: doesn't depend on any SSL library and doesn't install trusted CA certificates
 
 The following procedure illustrates how to compile all the *openwisp-config* variants and their dependencies:
@@ -261,7 +259,6 @@ The following procedure illustrates how to compile all the *openwisp-config* var
     echo "CONFIG_PACKAGE_openwisp-config-openssl=y" >> .config
     echo "CONFIG_PACKAGE_openwisp-config-mbedtls=y" >> .config
     echo "CONFIG_PACKAGE_openwisp-config-cyassl=y" >> .config
-    echo "CONFIG_PACKAGE_openwisp-config-polarssl=y" >> .config
     echo "CONFIG_PACKAGE_openwisp-config-nossl=y" >> .config
     make defconfig
     make tools/install