Remove special override for \perp...

in Text.TeXMath.Readers.TeX.Commands.  This caused `\perp` to
be read as U+22A5 instead of U+27C2.  This addresses the mismatch
with the TeX writer (which associates `\bot` with U+22A5 and
`\perp` with U+27C2).

Closes #247.

src/Text/TeXMath/Readers/TeX/Commands.hs

@@ -272,7 +272,6 @@ symbolMapOverrides = M.fromList
   , ("\\overbar",ESymbol Accent "\175")
   , ("\\overline",ESymbol TOver "\175")
   , ("\\overrightarrow",ESymbol Accent "\8407")
-  , ("\\perp",ESymbol Rel "\8869")
   , ("\\phi",EIdentifier "\981")
   , ("\\pi",EIdentifier "\960")
   , ("\\preceq",ESymbol Rel "\8828")