Deleting unwanted elements in lists of words

To make this post complete I have moved my comment here as an answer:

DeleteCases[ l, x_String /; StringContainsQ[x, "'" | "-" | NumberString ] , Infinity]

or

DeleteCases[l, _String?(StringContainsQ[#, "'" | "-" | NumberString ] &), Infinity]

Using RepeatedTiming reveals that the Condition version is minimally faster than the PatternTest version. It takes about 0.00021 secs on my machine. Note, that looking for patterns with head String only (e.g. _String) will speed up the process.

Alan's suggestion ( Select[LetterQ] /@ l ) is very concise and readable but will take twice as long (0.00041 secs) on my machine. Probably LetterQ does a bit more checks?

Update

kglr nicely shows how fast Pick is here and I linked an old post for those interested on why that may be. As LetterQ does more testing than the three Alternatives given above it may be worth mentioning that DigitCharacter as used by kglr also is faster than NumberString:

DeleteCases[l, x_String /; StringContainsQ[x, "'" | "-" | NumberString], Infinity] // RepeatedTiming // First

0.00020

DeleteCases[l, x_String /; StringContainsQ[x, "'" | "-" | NumberString], Infinity] // RepeatedTiming // First

0.00014

Pick[l, StringFreeQ["-" | "'" | DigitCharacter] /@ l]

{{"adventures", "in", "wonderland", "lewis", "carroll", "the", "millennium", "fulcrum", "edition", "chapter", "i", "down", "alice", "was", "beginning", "to", "get", "very", "tired", "of", "sitting", "by", "her", "sister", "on", "bank", "and", "having", "nothing", "do", "once", "or", "twice", "she", "had", "peeped", "into", "book", "reading", "but", "it", "no", "pictures", "conversations", "what", "is", "use", "a", "thought", "without", "conversation", "so", "considering", "own", "mind", "as", "well", "could", "for", "hot", "day", "made", "feel", "sleepy", "stupid", "whether", "pleasure", "making", "would", "be", "worth", "trouble", "getting", "up", "picking", "daisies", "when", "suddenly", "white", "rabbit", "with", "pink", "eyes", "ran", "close"},
{"there", "was", "nothing", "so", "very", "remarkable", "in", "that", "nor", "did", "alice", "think", "it", "much", "out", "of", "the", "way", "to", "hear", "rabbit", "say", "itself", "oh", "dear"}}}

This is several times faster than DeleteCases+StringContainsQ combination on input l:

Pick[l, StringFreeQ["-" | "'" | DigitCharacter] /@ l] // RepeatedTiming // First

0.000042

DeleteCases[l,  x_String /; StringContainsQ[x, "'" | "-" | NumberString], Infinity] //
  RepeatedTiming // First

0.00025