Revert "labs/yocto-first-build-stm32: use ready-made sstate"

This reverts commit 6391dbf.
Sharing the sstate cache in another way.

labs/yocto-first-build-stm32/yocto-first-build-stm32.tex

@@ -63,30 +63,6 @@ \section{Set up the build environment}
 \code{meta-openembedded/meta-oe}, \code{meta-openembedded/meta-python} and \code{meta-st-stm32mp} directory to the
 \code{BBLAYERS} variable.
 
-\section{Configure the reuse of prebuilt artifacts}
-
-On the STM32MP platform, the first build can take a very long time, in
-particular because of the need to build the Rust compiler to build
-Python cryptographic modules necessary to build the firmware (op-tee)
-binaries.
-
-Unless you have a very fast machine or plenty of time ahead of you, we
-recommend to configure your build so that it can reuse prebuilt
-artifacts. Such artifacts do not carry the risk to generate wrong
-binaries, because if they don't match the actual sources or build
-platform that you have, the binaries will be generated from source.
-
-This is one of the mechanisms that make BitBake run successive builds
-much faster, reusing binaries from previous runs whenever applicable.
-
-So add the below lines to your \code{conf/local.conf}:
-
-\begin{verbatim}
-BB_SIGNATURE_HANDLER = "OEEquivHash"
-BB_HASHSERVE = "auto"
-SSTATE_MIRRORS ?= "file://.* http://bootlin.com/yocto/sstate/stm32mp1/PATH;downloadfilename=PATH"
-\end{verbatim}
-
 \section{Build your first image}
 
 Now that you're ready to start the compilation, simply run: