Remove Go modules prepare command

Neither `go mod tidy` nor `go mod vendor` are necessary for Go modules
to function properly.

`go mod tidy` is a maintenance function for go.mod files and isn't
necessary for graph evaluation.

`go mod vendor` updates a vendor directory from the module cache, but if
the vendor directory isn't present, Go will simply download dependencies
to the module cache and evaluate the graph from there.

lib/license_finder/package_managers/go_modules.rb

@@ -12,10 +12,6 @@ def takes_priority_over
       end
     end
 
-    def prepare_command
-      'GO111MODULE=on go mod tidy && GO111MODULE=on go mod vendor'
-    end
-
     def active?
       mod_files?
     end

spec/lib/license_finder/package_managers/go_modules_spec.rb

@@ -79,12 +79,6 @@ module LicenseFinder
       end
     end
 
-    describe '.prepare_command' do
-      it 'returns the correct package management command' do
-        expect(subject.prepare_command).to eq('GO111MODULE=on go mod tidy && GO111MODULE=on go mod vendor')
-      end
-    end
-
     describe '.takes_priority_over' do
       it 'returns the package manager it takes priority over' do
         expect(described_class.takes_priority_over).to eq(Go15VendorExperiment)