sage.structure, sage.sets: Remove hard dependencies on the symbolic ring / polynomial rings

[mkoeppe]

(partially cherry-picked from #32432)

CC: @tscrim @kliem

Component: refactoring

Author: Matthias Koeppe

Branch/Commit: 73aabd2

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/32599

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1 +1,2 @@
+(cherry-picked from #32432)
 

[mkoeppe]

Branch: u/mkoeppe/sage_structure__sage_sets__remove_hard_dependencies_on_the_symbolic_ring___polynomial_rings

[mkoeppe]

New commits:

8e27fdc	src/sage/structure/sequence.py: Do not fail if polynomial rings cannot be imported
b43a50c	src/sage/sets/condition_set.py: Do not fail if sage.symbolic cannot be imported

[mkoeppe]

Commit: b43a50c

[mkoeppe]

Author: Matthias Koeppe

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1,2 +1,2 @@
-(cherry-picked from #32432)
+(partially cherry-picked from #32432)
 

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

73aabd2

src/sage/sets/condition_set.py: Fix up import

[sagetrac-git]

Changed commit from b43a50c to 73aabd2

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:8

LGTM.

[mkoeppe]

comment:9

Thank you!

[vbraun]

Changed branch from u/mkoeppe/sage_structure__sage_sets__remove_hard_dependencies_on_the_symbolic_ring___polynomial_rings to 73aabd2