Refactor: remove analysis scripts (#305)

### Summary
This PR is the first part of the "layout analysis" refactor to move it
from unstructured-inference repo to unstructured repo. This PR removes
"layout analysis" related code from unstructured-inference repo and
works together with the unstructured refactor PR -
Unstructured-IO/unstructured#2273.

This PR also adds a few more test cases for `layoutelement.py` to make
coverage to over 95%.

Author: christinestraub

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.7.37-dev0
+
+* refactor: remove layout analysis related code
+
 ## 0.7.36
 
 fix: add input parameter validation to `fill_cells()` when converting cells to html