net: buf: remove data from end of buffer

[JordanYates]

Is your enhancement proposal related to a problem? Please describe.

The net/buf.h API currently implements the following functionality:

data location	data operation	API
buffer start	add	net_buf_push_*
	remove	net_buf_pull_*
buffer end	add	net_buf_add_*
	remove	???

I propose to add an implementation for the final category of operations.

Describe the solution you'd like

A set of functions that provides the same functionality as net_buf_pull_*, but from the end of the buffer.
As push and pull are opposites in terms of naming, I propose net_buf_remove_* as the opposite of net_buf_add_*.

Describe alternatives you've considered
N/A