Revert "SONAR-4753 Modify the technical debt density calculation"

This reverts commit fed100c4c662cc78b857d12b1e0968b1e664de6b.
Revert "SONAR-4717 Add technical_debt_density in Technical Debt widget"

This reverts commit b288cca1db46743ed67056b6e962420dd1855d1e.
Revert "SONAR-4753 Compute the new "Technical Debt Density" metric"

This reverts commit 5e91ad15421776a8ae778c4a49a5118c7ec214a4.
Revert SONAR-4753
SONAR-4717 Display "Technical Debt" in the Issues widget