README: Remove 'all run' target

Only QEMU and FVP have a 'run' target but all *.md files refer to README
Section 7.5 which calls for 'make all run'. Remove this target since
qemu.md and fvp.md already mention it. Also, 'all' should be the default
target so 'make' should be enough.

Fixes: https://github.com/OP-TEE/build/issues/146


Signed-off-by: Victor Chong <victor.chong@linaro.org>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>

README.md

@@ -163,7 +163,7 @@ symlink the `Makefile` to the correct device specific makefile, that means that
 you simply start the build by running:
 
 ```bash
-$ make all run
+$ make
 ```
 This step will also take some time, but you can speed up subsequent builds by
 enabling [ccache] (again see Tips and Tricks).