build/pkgs: drop obsolete simplegeneric package

This package was a dependency of ipython, but has not been required
for some time:

  ipython/ipython@6d9a28a2

Author: orlitzky

build/pkgs/ipython/dependencies

@@ -1,4 +1,4 @@
-tornado pyzmq pickleshare simplegeneric traitlets decorator wcwidth prompt_toolkit pygments pexpect appnope backcall jedi stack_data | $(PYTHON_TOOLCHAIN) $(PYTHON)
+tornado pyzmq pickleshare traitlets decorator wcwidth prompt_toolkit pygments pexpect appnope backcall jedi stack_data | $(PYTHON_TOOLCHAIN) $(PYTHON)
 
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