Remove API reference (#2270)

Author: VeckoTheGecko

docs/reference.rst

@@ -1,14 +1,6 @@
 Parcels API
 ===================================
 
-.. toctree::
-  :maxdepth: 2
+.. note::
 
-  Fieldsets and Fields <reference/fields>
-  Particles and particle sets <reference/particles>
-  Particlefile <reference/particlefile>
-  Predefined Kernels <reference/predefined_kernels>
-  User-defined Kernels <reference/userdefined_kernels>
-  Particle-particle interaction <reference/interaction>
-  Gridsets and grids <reference/grids>
-  Miscellaneous <reference/misc>
+   This section is a work in progress.