Revert "Merge branch 'build_ext' into 'master'"

This reverts merge request !32965 (merged)

Caching the externals build causes problems when changing the upstream project version: ATLINFR-3018

merged

mentioned in commit ce976319

This merge request affects 3 packages:

• Projects/AthGeneration
• Projects/AthSimulation
• Projects/Athena

Adding @jchapman ,@vpascuzz ,@akraszna ,@rbianchi as watchers

added Build master review-pending-level-1 labels

Merged immediately as this blocked all CI builds.

mentioned in merge request !33208 (merged)

CI Result SUCCESS (hash 38760d65)

	Athena	AthSimulation	AnalysisBase	AthGeneration
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 14643]

added sweep:ignore label