Fix bug where removal of tag prop wouldn't update Node

[jnwatson]

Fix issue where removing a tag prop e.g. [ -#foo:score ] would still have the tagprop returned in the Node.

[codecov]

Codecov Report

Merging #1454 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1454      +/-   ##
==========================================
- Coverage   95.39%   95.37%   -0.02%     
==========================================
  Files         133      133              
  Lines       20469    20468       -1     
==========================================
- Hits        19526    19521       -5     
- Misses        943      947       +4

Flag	Coverage Δ
#linux	95.37% <100%> (+0.01%)	⬆️
#osx	?

Impacted Files	Coverage Δ
synapse/lib/node.py	98.68% <100%> (-0.01%)	⬇️
synapse/lib/platforms/darwin.py	0% <0%> (-100%)	⬇️
synapse/lib/thisplat.py	58.33% <0%> (-8.34%)	⬇️
synapse/lib/link.py	98.54% <0%> (-0.73%)	⬇️
synapse/lib/lmdbslab.py	98.91% <0%> (-0.16%)	⬇️
synapse/lib/base.py	92.05% <0%> (+0.99%)	⬆️

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