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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 76.47059% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 78.07%. Comparing base (dbff1ff) to head (d6b886f). Report is 80 commits behind head on master.

Files	Patch %	Lines
galgebra/metric.py	0.00%	9 Missing :warning:
galgebra/dop.py	54.54%	5 Missing :warning:
galgebra/ga.py	0.00%	2 Missing :warning:
galgebra/lt.py	80.00%	2 Missing :warning:
galgebra/mv.py	90.47%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #452 +/- ## ========================================== - Coverage 78.87% 78.07% -0.80% ========================================== Files 17 18 +1 Lines 4189 4169 -20 ========================================== - Hits 3304 3255 -49 - Misses 885 914 +29 ```

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[utensil]

Thank you, @eric-wieser , this should be superseded by #510 which merged gprinter from upstream. Feel free to reopen if there are remaining issues.