Eliminate npm tests (RIPD-1369)

Remove mention of npm tests in developer docs. Eliminate `npm test` from
automation and ci scripts.

Builds/ArchLinux/PKGBUILD

@@ -9,7 +9,6 @@ url="https://github.com/ripple/rippled"
 license=('custom:ISC')
 depends=('protobuf' 'openssl' 'boost-libs')
 makedepends=('git' 'scons' 'boost')
-checkdepends=('nodejs')
 backup=("etc/$pkgname/rippled.cfg")
 source=("git://github.com/ripple/rippled.git#branch=master")
 sha512sums=('SKIP')
@@ -26,8 +25,6 @@ build() {
 
 check() {
 	cd "$srcdir/$pkgname"
-	npm install
-	npm test
 	build/rippled --unittest
 }