chore(scss): remove injected global styles (#26469)

this commit removes a globally injected style, `ionic.skip-warns.scss`,
from the project. this stylesheet was used to set a variable, `$Ionic`,
that would turn on/off deprecation warnings in (the also removed)
`ionic.deprecation.scss`. any file using either of the aforementioned
files have been updated.

this change is occurring while the stencil team is looking to improve
the size of generated components that use >1 mode. this deprecation was
a part of an initiative to remove sass source files from artifact
published to npm. while that was completed, this deprecation was not
removed (until now)

Co-authored-by: Liam DeBeasi <liamdebeasi@users.noreply.github.com>

core/src/themes/ionic.functions.string.scss

@@ -1,5 +1,3 @@
-@import "./ionic.deprecation";
-
 // String Utility Functions
 // --------------------------------------------------------------------------------