Remove duplicated "Composition Functions" concept (#742)

* Removed duplicate concept

Signed-off-by: Alexander Pashkov <[email protected]>

* Removed duplicate concept in the master

Signed-off-by: Alexander Pashkov <[email protected]>

---------

Signed-off-by: Alexander Pashkov <[email protected]>
Co-authored-by: Alexander Pashkov <[email protected]>

Author: cyphysical

content/master/concepts/_index.md

@@ -70,11 +70,6 @@ building and managing external resources through Kubernetes.
   custom resource mapping or storing and retrieving data across Claims and
   Composite Resources. 
 
-* [**Composition functions**]({{<ref "./composition-functions">}}) are a container
-  of your own custom code which can read, write and change any Crossplane
-  resource. Composition functions are incredibly powerful tools allowing for
-  loops and conditional patching or resource generation.
-
 * [**Usages**]({{<ref "./usages">}}) defining critical resources or custom
   dependency mappings. Usages can prevent Crossplane from deleting or can
   ensure that a parent resource waits for Crossplane to delete all child 

content/v1.14/concepts/_index.md

@@ -70,11 +70,6 @@ building and managing external resources through Kubernetes.
   custom resource mapping or storing and retrieving data across Claims and
   Composite Resources. 
 
-* [**Composition functions**]({{<ref "./composition-functions">}}) are a container
-  of your own custom code which can read, write and change any Crossplane
-  resource. Composition functions are incredibly powerful tools allowing for
-  loops and conditional patching or resource generation.
-
 * [**Usages**]({{<ref "./usages">}}) defining critical resources or custom
   dependency mappings. Usages can prevent Crossplane from deleting or can
   ensure that a parent resource waits for Crossplane to delete all child 

content/v1.15/concepts/_index.md

@@ -70,11 +70,6 @@ building and managing external resources through Kubernetes.
   custom resource mapping or storing and retrieving data across Claims and
   Composite Resources. 
 
-* [**Composition functions**]({{<ref "./composition-functions">}}) are a container
-  of your own custom code which can read, write and change any Crossplane
-  resource. Composition functions are incredibly powerful tools allowing for
-  loops and conditional patching or resource generation.
-
 * [**Usages**]({{<ref "./usages">}}) defining critical resources or custom
   dependency mappings. Usages can prevent Crossplane from deleting or can
   ensure that a parent resource waits for Crossplane to delete all child