Remove unsupported variables.go reference from README

The reference to `variables.go` in the README was removed because it is
not supported. There were not enough use cases to justify its presence.

Fixes bwplotka#141

get.go

@@ -817,7 +817,6 @@ This is directory which stores Go modules with pinned buildable package that is
 * Run ` + "`" + "bingo get <tool>" + "`" + ` to install <tool> that have own module file in this directory.
 * For Makefile: Make sure to put ` + "`" + "include %s/Variables.mk" + "`" + ` in your Makefile, then use $(<upper case tool name>) variable where <tool> is the %s/<tool>.mod.
 * For shell: Run ` + "`" + "source %s/variables.env" + "`" + ` to source all environment variable for each tool.
-* For go: Import ` + "`" + "%s/variables.go" + "`" + ` to for variable names.
 * See https://github.com/bwplotka/bingo or -h on how to add, remove or change binaries dependencies.
 
 ## Requirements