UnXFAIL Wester test_I1 with nsimplify
UnXFAIL Wester test_I2 with nsimplify
UnXFAIL Wester test_K2 with nsimplify
UnXFAIL Wester test_M2
Get rid of nsimplify: test_C14, test_C15
Revert "UnXFAIL Wester test_I1 with nsimplify"

This reverts commit 3f29ef613e354bdeea87bd18a5e6f1bfe70d79b4.
Revert "UnXFAIL Wester test_I2 with nsimplify"

This reverts commit 61f065ad9ca06f567777a054bf7bce64d6dd2938.
Revert "UnXFAIL Wester test_K2 with nsimplify"

This reverts commit c648253cb69df6f4f3e1e6fe76159b98ea253600.
Merge branch 'master' into wester-nsimplify
Get rid of nsimplify: fix test_C17 with radsimp
Get rid of nsimplify: fix test_C18
Get rid of nsimplify: convert nsimplify -> simplify and mark tests as XFAILed
Merge pull request #2353 from skirpichev/wester-nsimplify

UnXFAIL Wester test_M2 and get rid of using nsimplify