I would like to implement a function with
removeRS('Hoy estoy tristeeeeeee')
Hoy estoy triste
I did not think very carefully on this, but this is my quick solution using references in regular expressions:
gsub('([[:alpha:]])\\1+', '\\1', 'Buenaaaaaaaaa Suerrrrte') #  "Buena Suerte"
() captures a letter first,
\\1 refers to that letter,
+ means to match it once or more; put all these pieces together, we can match a letter two or more times.
To include other characters besides alphanumerics, replace
[[:alpha:]] with a regex matching whatever you wish to include.