Reconsider the dependency on silex.sile introduced in 1.1.0

[Omikhleia]

In 1.1.0 we relied on SILE's scalebox package introduced in 0.14.9 and introduced silex.sile as compatibility layer.

In sile-typesetter/sile#1866 I wrote:

textsubsuper.sile = does depend on silex, but sile-typesetter/sile#1853 would make it unnecessary.

Actually we might not care:

• Update README to state we support SILE 0.14.13 or upper
• Remove the shims and let "scalebox" be responsible for it.
• When used with resilient, the latter still loads silex and currently replaces its implementation of scalebox. For obvious reasons this will stay this way until 0.15 at best.

In other terms, people should be safe using this module outside of resilient, and inside resilient they already get the shims for bleed etc.

--> Removal of the dependency here should be fine...