Replace integration tests with unit tests

[cjbarth]

Description

Several tests made use of the deprecated requests package. This removes all the tests that relied on that and replaces them with unit tests.

Checklist:

• Issue Addressed: [ resolves [BUG] test failure in 3.2.0 in "captured SAML requests / Logout" in capturedSamlRequests.ts #668 ]
• Link to SAML spec: [ n/a ]
• Tests included? [ yes ]
• Documentation updated? [ n/a ]

[markstos]

If the amount of code coverage is the same, and we are able to drop several dependencies, this seems like a win.

Integration tests have value, but that value has to be weighed against their cost.

[cjbarth]

Before this PR:

----------------------|---------|----------|---------|---------|--------------------------------------------------------
File                  | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------------------|---------|----------|---------|---------|--------------------------------------------------------
All files             |   73.33 |     68.1 |   70.58 |   73.33 |
 index.ts             |     100 |      100 |     100 |     100 |
 multiSamlStrategy.ts |   87.87 |       75 |    87.5 |   87.87 | 45,61,78,98
 strategy.ts          |   68.18 |     67.3 |   63.63 |   68.18 | ...163,170-174,184,190,209-220,226,234-241,249,257,271
 types.ts             |       0 |      100 |       0 |       0 | 50
----------------------|---------|----------|---------|---------|--------------------------------------------------------

After this PR:

----------------------|---------|----------|---------|---------|--------------------------------------------------------
File                  | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------------------|---------|----------|---------|---------|--------------------------------------------------------
All files             |   80.53 |    75.43 |   77.14 |   80.53 |
 index.ts             |     100 |      100 |     100 |     100 |
 multiSamlStrategy.ts |   87.87 |       75 |    87.5 |   87.87 | 45,61,78,98
 strategy.ts          |   77.98 |    75.49 |   73.91 |   77.98 | ...152,161,163,174,179,184,190,210,221,232,246,254,260
 types.ts             |       0 |      100 |       0 |       0 | 50
----------------------|---------|----------|---------|---------|--------------------------------------------------------