Remove Yotta support from the docs, tests and build scripts

Yotta is no longer supported by Mbed TLS, so has been removed. Specifically, the
following changes have been made:
 * references to yotta have been removed from the main readme and build
   instructions
 * the yotta module directory and build script has been removed
 * yotta has been removed from test scripts such as all.sh and check-names.sh
 * yotta has been removed from other files that that referenced it such as the
   doxyfile and the bn_mul.h header
 * yotta specific configurations and references have been removed from config.h
diff --git a/doxygen/mbedtls.doxyfile b/doxygen/mbedtls.doxyfile
index 2a87ada..6be7263 100644
--- a/doxygen/mbedtls.doxyfile
+++ b/doxygen/mbedtls.doxyfile
@@ -696,7 +696,7 @@
 # Note that relative paths are relative to the directory from which doxygen is
 # run.
 
-EXCLUDE                = ../configs ../yotta/module
+EXCLUDE                = ../configs
 
 # The EXCLUDE_SYMLINKS tag can be used to select whether or not files or
 # directories that are symbolic links (a Unix file system feature) are excluded