man: Mention neither `HOMEBREW_DEBUG_INSTALL` nor `HOMEBREW_DEBUG_PREFIX` any

more.

     `brew`'s `man` page's 'ENVIRONMENT' section is intended to list only those
environment variables that users can set, not any that Homebrew sets as part of
its operation.

Library/Homebrew/manpages/brew.1.md.erb

@@ -159,16 +159,6 @@ Note that environment variables must have a value set to be detected. For exampl
   * `HOMEBREW_DEBUG`:
     If set, any commands that can emit debugging information will do so.
 
-  * `HOMEBREW_DEBUG_INSTALL`:
-    When `brew install -d` or `brew install -i` drops into a shell,
-    `HOMEBREW_DEBUG_INSTALL` will be set to the name of the formula being
-    brewed.
-
-  * `HOMEBREW_DEBUG_PREFIX`:
-    When `brew install -d` or `brew install -i` drops into a shell,
-    `HOMEBREW_DEBUG_PREFIX` will be set to the target prefix in the Cellar
-    of the formula being brewed.
-
   * `HOMEBREW_DEVELOPER`:
     If set, Homebrew will tweak behaviour to be more relevant for Homebrew
     developers (active or budding) e.g. turning warnings into errors.

docs/Manpage.md

@@ -1160,16 +1160,6 @@ Note that environment variables must have a value set to be detected. For exampl
   * `HOMEBREW_DEBUG`:
     If set, any commands that can emit debugging information will do so.
 
-  * `HOMEBREW_DEBUG_INSTALL`:
-    When `brew install -d` or `brew install -i` drops into a shell,
-    `HOMEBREW_DEBUG_INSTALL` will be set to the name of the formula being
-    brewed.
-
-  * `HOMEBREW_DEBUG_PREFIX`:
-    When `brew install -d` or `brew install -i` drops into a shell,
-    `HOMEBREW_DEBUG_PREFIX` will be set to the target prefix in the Cellar
-    of the formula being brewed.
-
   * `HOMEBREW_DEVELOPER`:
     If set, Homebrew will tweak behaviour to be more relevant for Homebrew
     developers (active or budding) e.g. turning warnings into errors.

manpages/brew.1

@@ -1283,14 +1283,6 @@ If set, Homebrew will pass \fB\-\-verbose\fR when invoking \fBcurl\fR(1)\.
 If set, any commands that can emit debugging information will do so\.
 .
 .TP
-\fBHOMEBREW_DEBUG_INSTALL\fR
-When \fBbrew install \-d\fR or \fBbrew install \-i\fR drops into a shell, \fBHOMEBREW_DEBUG_INSTALL\fR will be set to the name of the formula being brewed\.
-.
-.TP
-\fBHOMEBREW_DEBUG_PREFIX\fR
-When \fBbrew install \-d\fR or \fBbrew install \-i\fR drops into a shell, \fBHOMEBREW_DEBUG_PREFIX\fR will be set to the target prefix in the Cellar of the formula being brewed\.
-.
-.TP
 \fBHOMEBREW_DEVELOPER\fR
 If set, Homebrew will tweak behaviour to be more relevant for Homebrew developers (active or budding) e\.g\. turning warnings into errors\.
 .