Drop Custom Projection support

[scothis]

The Custom Projection extension was dropped from the Service Binding
spec. We no longer need to maintain it.

The ServiceBindingProjection resource is still used to manage the
binding, but it has moved into the internal.bindings.labs.vmware.com API
group and is now an implementation detail rather than a supported
interface.

Refs servicebinding/spec#143
Resolves #118

[codecov]

Codecov Report

Merging #123 (043ea8b) into main (c610b7e) will increase coverage by 0.69%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #123      +/-   ##
==========================================
+ Coverage   91.50%   92.20%   +0.69%     
==========================================
  Files          18       17       -1     
  Lines         577      539      -38     
==========================================
- Hits          528      497      -31     
+ Misses         28       24       -4     
+ Partials       21       18       -3     

Impacted Files	Coverage Δ
pkg/apis/labsinternal/v1alpha1/register.go	100.00% <ø> (ø)
...nternal/v1alpha1/servicebindingprojection_types.go	100.00% <ø> (ø)
...is/servicebinding/v1alpha2/servicebinding_types.go	100.00% <ø> (ø)
pkg/reconciler/servicebinding/controller.go	100.00% <ø> (ø)
...nal/v1alpha1/servicebindingprojection_lifecycle.go	100.00% <100.00%> (ø)
...ervicebinding/v1alpha2/servicebinding_lifecycle.go	100.00% <100.00%> (ø)
...rvicebinding/resources/servicebindingprojection.go	100.00% <100.00%> (ø)
pkg/reconciler/servicebinding/servicebinding.go	75.92% <100.00%> (ø)
.../reconciler/servicebindingprojection/controller.go	57.14% <100.00%> (-5.36%)	⬇️

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