Evict RiemannSolver interface

Cleanup effort to convert all projects to the newer @with_signature broadcasting interface.

Cleansed:

• ScalarEq
• EulerEq
• SRHD -- need ref tests first
• GRHD -- disabled for now, so can be ignored

added refactor label

added 6 commits

• 7c691768 - evict old broadcasting methods
• b1672f8c - re-enable srhd_smooth test
• fa3346bb - convert all in ScalarEq
• 9028a52d - convert all in EulerEq
• f8340056 - evict Riemann solver related stuff from ScalarEq
• ae814ba3 - evict Riemann solver related stuff from EulerEq

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added 1 commit

• c286660e - evict Riemann solver related stuff from SRHD

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added 1 commit

• 486eea48 - evict riemannsolver.jl and broadcast_[volume,faces,bdry]!

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marked the checklist item SRHD -- need ref tests first as completed

added 1 commit

• 48162a38 - remove non-existent export

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enabled an automatic merge when the pipeline for 48162a38 succeeds

aborted the automatic merge because source branch was updated

added 1 commit

• 76374136 - remove more Riemann solver stuff

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merged

mentioned in commit 8c450bb9

mentioned in commit e71adc35

mentioned in issue #65 (closed)