Refactor: libcrmcommon: Drop pcmk__trim()

Use g_strchomp() instead. The two functions are not equivalent.
pcmk__trim() strips trailing newlines, while g_strchomp() strips
all trailing whitespace. However, for the use cases we have,
g_strchomp() is fine.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>