remove unnecessary \up (upright) from some latex abbrevs (e.g. \upM…

…u -> \Mu) (JuliaLang#50925)

Closes JuliaLang#50911.  Closes JuliaLang#50913.

There were a few oddball symbols prefixed with `\up` (for "upright") for
no reason that I can tell, ala the LaTeX "upgreek" package, even though
we don't use an `\up` prefix for other upright Greek letters (e.g. we
have `\alpha`, not `\upalpha`, even though it isn't italicized — we have
`\italpha` for italic alpha).

Not breaking since this is just a UI thing.

(In practice, I doubt many people use these symbols. e.g. `\upMu` is
`Μ`, which looks a lot like the Latin `M`. But there is no reason to
have the `\up` prefix here. It seems to have just been an automated
abbreviation-import snafu. And [`\upkoppa 'ϟ'`
(U+O3DF)](https://www.compart.com/en/unicode/U+03DF) is visually quite
distinctive though I've never seen it used in math, not to mention
lowercase — it's definitely goofy to have an `\up` prefix for it.)

stdlib/REPL/src/latex_symbols.jl

@@ -984,17 +984,16 @@ const latex_symbols = Dict(
  "\\droang" => "̚", # left angle above (non-spacing)
  "\\wideutilde" => "̰", # under tilde accent (multiple characters and non-spacing)
  "\\not" => "̸", # combining long solidus overlay
- "\\upMu" => "Μ", # capital mu, greek
- "\\upNu" => "Ν", # capital nu, greek
- "\\upOmicron" => "Ο", # capital omicron, greek
- "\\upepsilon" => "ε", # rounded small epsilon, greek
- "\\upomicron" => "ο", # small omicron, greek
- "\\upvarbeta" => "ϐ", # rounded small beta, greek
- "\\upoldKoppa" => "Ϙ", # greek letter archaic koppa
- "\\upoldkoppa" => "ϙ", # greek small letter archaic koppa
- "\\upstigma" => "ϛ", # greek small letter stigma
- "\\upkoppa" => "ϟ", # greek small letter koppa
- "\\upsampi" => "ϡ", # greek small letter sampi
+ "\\Mu" => "Μ", # capital mu, greek
+ "\\Nu" => "Ν", # capital nu, greek
+ "\\Omicron" => "Ο", # capital omicron, greek
+ "\\omicron" => "ο", # small omicron, greek
+ "\\varbeta" => "ϐ", # rounded small beta, greek
+ "\\oldKoppa" => "Ϙ", # greek letter archaic koppa
+ "\\oldkoppa" => "ϙ", # greek small letter archaic koppa
+ "\\stigma" => "ϛ", # greek small letter stigma
+ "\\koppa" => "ϟ", # greek small letter koppa
+ "\\sampi" => "ϡ", # greek small letter sampi
  "\\tieconcat" => "⁀", # character tie, z notation sequence concatenation
  "\\leftharpoonaccent" => "⃐", # combining left harpoon above
  "\\rightharpoonaccent" => "⃑", # combining right harpoon above