delete obsolete STM shielding Poly

[sdifalco]

Following request from Yongyi.
New STM geometry configuration file (v10) created
All geometry configuration files changed.

[FNALbuild]

Hi @sdifalco,
You have proposed changes to files in these packages:

• Mu2eG4

which require these tests: build.

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⌛ The following tests have been triggered for d53f259: build (Build queue - API unavailable)

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[FNALbuild]

☀️ The build tests passed at d53f259.

Test	Result	Details
test with	✅	Command did not list any other PRs to include
merge	✅	Merged d53f259 at 38f6943
build (prof)	✅	Log file. Build time: 04 min 35 sec
ceSimReco	✅	Log file.
g4test_03MT	✅	Log file.
transportOnly	✅	Log file.
POT	✅	Log file.
g4study	✅	Log file.
cosmicSimReco	✅	Log file.
cosmicOffSpill	✅	Log file.
ceSteps	✅	Log file.
ceDigi	✅	Log file.
muDauSteps	✅	Log file.
ceMix	✅	Log file.
rootOverlaps	✅	Log file.
g4surfaceCheck	✅	Log file.
trigger	✅	Log file.
check_cmake	✅	Log file.
FIXME, TODO	✅	TODO (0) FIXME (0) in 0 files
clang-tidy	✅	0 errors 0 warnings
whitespace check	✅	no whitespace errors found

N.B. These results were obtained from a build of this Pull Request at d53f259 after being merged into the base branch at 38f6943.

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[YongyiBWu]

I think run2 geometry will still have the poly. The only reason it is removed from run1 geometry is because the external shielding downstream blocks are removed in run1. The poly is embedded in the blocks so it cannot float in the air. For run2 geometry the shielding blocks are still there so there is no need to change this file.

[YongyiBWu]

I believe the change does not apply to Mu2eG4/geom/geom_run2.txt. All the rest changes are good.