remove useless unset()s

there is mightily little point in unsetting variables right before
unconditionally assigning to them.

Change-Id: I24c1814ce38bf9aab4496679b1a670f3cd55c536
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

mkspecs/features/exclusive_builds.prf

@@ -1,9 +1,6 @@
 # fixExclusiveOutputDirs(1config, 2config)
 # Change all output paths that references 2config to have the string 1config in them
 defineTest(fixExclusiveOutputDirs) {
-    unset(firstBuild)
-    unset(secondBuild)
-    unset(appendFirstBuild)
     firstBuild = $$1
     secondBuild = $$2
     count(ARGS, 2, greaterThan):isEqual($$list($$lower($$3)), false):appendFirstBuild = false
@@ -29,11 +26,6 @@ defineTest(fixExclusiveOutputDirs) {
 # addExclusiveBuilds(1config, 1name, 2config, 2name)
 # Adds two BUILDS which are exclusive to each other.
 defineTest(addExclusiveBuilds) {
-    unset(firstBuild)
-    unset(firstBuildName)
-    unset(secondBuild)
-    unset(secondBuildName)
-
     firstBuild = $$1
     firstBuildName = $$2
     secondBuild = $$3

mkspecs/features/qt_functions.prf

@@ -9,7 +9,6 @@ defineReplace(qtPlatformTargetSuffix) {
 }
 
 defineReplace(qtLibraryTarget) {
-   unset(LIBRARY_NAME)
    LIBRARY_NAME = $$1
    mac:!static:contains(QT_CONFIG, qt_framework) {
       QMAKE_FRAMEWORK_BUNDLE_NAME = $$LIBRARY_NAME

src/angle/src/config.pri

@@ -21,7 +21,6 @@ win32 {
 }
 
 defineReplace(addGnuPath) {
-    unset(gnuPath)
     gnuPath = $$1
     !isEmpty(gnuPath):!isEmpty(GNUTOOLS) {
         gnuPath = $${GNUTOOLS} && $$gnuPath