Remove all dependencies on galgebra.printer

[eric-wieser]

This means that the print customizations are now completely optional, and only take effect if import galgebra.printer is used. This is a good idea because these customizations may be surprising, as they:

• Replace the builtin print function
• Monkey-patch parts of sympy

This type of surprise should be opted into (by choosing to import this module), not automatic.

[lgtm-com[bot]]

This pull request introduces 1 alert when merging abda1e6a43ae39ddca453ecdea4dca10f0705531 into eb8ccd22c8ce865b985925ff2c22fda3a766891a - view on LGTM.com

new alerts:

• 1 for Unused import