devel/electron42: Use esbuild binary provided by npm package registry

The chromium upstream expects a specific version of esbuild for
building, which is sometimes different from the one we have in the
ports tree. To prevent such a discrepancy, always use the binary of
the same version as the upstream one which is provided by the npm
package registry.

Reported by: Andrea Venturoli <ml@netfence.it> (via ports)