Drop "cascading" and "private" dependency from the lexicon

This is no longer a meaningful distinction.

Author: CodaFi

docs/DependencyAnalysis.md

@@ -56,33 +56,6 @@ Note:
 > may change its members drastically.
 
 
-Cascading vs. Non-Cascading Dependencies
-========================================
-
-If file A depends on file B, and file B depends on file C, does file A depend
-on file C? The answer is: maybe! It depends how file B is using file C. If all
-uses are inside function bodies, for example, then changing file C only
-requires rebuilding file B, not file A. The terminology here is that file B has
-a *non-cascading* dependency on file C.
-
-By contrast, if changing file C affects the interface of file B, then the
-dependency is said to be *cascading,* and changing file C would require
-rebuilding both file B and file A.
-
-The various dependency tracking throughout the compiler will look at the
-context in which information is being used and attempt to determine whether or
-not a particular dependency should be considered cascading. If there's not
-enough context to decide, the compiler has to go with the conservative choice
-and record it as cascading.
-
-
-Note:
-
-> In the current on-disk representation of dependency information, cascading
-> dependencies are the default. Non-cascading dependencies are marked
-> `private` by analogy with the Swift `private` keyword.
-
-
 External Dependencies
 =====================
 

docs/Lexicon.md

@@ -100,18 +100,6 @@ These can usually be directly compared to test whether two types are the
 same; the exception is when generics get involved. In this case you'll need
 a [generic environment](#generic-environment). Contrast with [sugared type](#sugared-type).
 
-## cascading dependency
-
-A kind of dependency edge relevant to the incremental name tracking
-subsystem. A cascading dependency (as opposed to a
-[private dependency](#private-dependency) requires the Swift driver to
-transitively consider dependency edges in the file that defines the used
-name when incremental compilation is enabled. A cascading dependency is much
-safer to produce than its private counterpart, but it comes at the cost of
-increased usage of compilation resources - even if those resources are being
-wasted on rebuilding a file that didn't actually require rebuilding.
-See [DependencyAnalysis.md](DependencyAnalysis.md).
-
 ## Clang importer
 
 The part of the compiler that reads C and Objective-C declarations and
@@ -452,18 +440,6 @@ The file currently being compiled, as opposed to the other files that are
 only needed for context. See also
 [Whole-Module Optimization](#wmo-whole-module-optimization).
 
-## private dependency
-
-A kind of dependency edge relevant to the incremental name tracking
-subsystem. A private dependency (as opposed to a
-[cascading dependency](#cascading-dependency)) declares a dependency edge
-from one file to a name referenced in that file that does not
-require further transitive evaluation of dependency edges by the Swift
-driver. Private dependencies are therefore cheaper than cascading
-dependencies, but must be used with the utmost care or dependent files will
-fail to rebuild and the result will most certainly be a miscompile.
-See [DependencyAnalysis](DependencyAnalysis.md).
-
 ## QoI
 
 "Quality of implementation." The term is meant to describe not how