remove wrong and now useless variable declaration in Makefile
Created by: valentinThomazic
Related to https://github.com/openhwgroup/cva6/issues/1572 and https://github.com/openhwgroup/cva6/issues/1569 .
Setting VERILATOR_INSTALL_DIR
in the ./Makefile
is not relevant anymore since it now has to be set before running CVA.py to simulate which will then use the Makefile.
On top of that, the path is wrong (should be ./tools
not ./tmp
).