Remove Makefile rule clean-dev
From npm ci docs https://docs.npmjs.com/cli/v7/commands/npm-ci:
If a node_modules is already present, it will be automatically removed
before npm ci begins its install.
Unnecessary since b595d86e96a518c36c1889a338053512ffbb13fa.
Signed-off-by: François Freitag <mail@franek.fr>