C++: More IR reshuffling

Remove redundant "_ir" suffix.
Move non-user-importable modules into "implementation" directory.

Author: dave-bartolomeo

cpp/ql/src/semmle/code/cpp/ir/IR.qll

@@ -1,3 +1,3 @@
 // Most queries should operate on the aliased SSA IR, so that's what we expose
 // publically as the "IR".
-import internal.aliased_ssa_ir.IR
+import internal.aliased_ssa.IR

cpp/ql/src/semmle/code/cpp/ir/IRSanity.ql

@@ -5,4 +5,4 @@
  * @id cpp/ir-sanity-check
  */
 
-import internal.aliased_ssa_ir.IRSanity
+import internal.aliased_ssa.IRSanity

cpp/ql/src/semmle/code/cpp/ir/Opcode.qll

@@ -5,4 +5,4 @@
  * @kind graph
  */
 
-import internal.aliased_ssa_ir.PrintIR
+import internal.aliased_ssa.PrintIR

cpp/ql/src/semmle/code/cpp/ir/PrintIR.ql

@@ -1,5 +1,5 @@
 import cpp
-private import internal.TempVariableTag
+private import semmle.code.cpp.ir.internal.TempVariableTag
 
 class TempVariableTag extends TTempVariableTag {
   string toString() {